# Number System : Aptitude Test (200 Questions with Explanation)

• Formulas:-
0, 1, 2, 3, ----9. are called digits.
10, 11, 12,----- are called Number.

Natural number (N) :-
Counting numbers are called natural numbers.
Example:- 1, 2, 3,---etc. are all natural numbers. minimum natural number 1 and maximum natural number ∞

Whole numbers (W) :-
All counting numbers together with zero from the set of whole numbers
Example:- 0, 1, 2, 3, 4, ------ are whole number.

Integers (Z) :-
All counting numbers, 0 and -ve of counting numbers are called integers.
Example:- -∞---------, -3, -2, -1, 0, 1, 2, 3, -------∞

Rational Numbers (Q) :-
A Rational Number is a real number that can be written as a simple fraction
Example:- {p/q/p,q∈Z}

Irrational NUmbers :-
An Irrational Number is a real number that cannot be written as a simple fraction.
Example:- √

Even numbers :-
A number divisible by 2 is called an even number.
Example:- 0, 2, 4, 6, - - - - - - - - -

Odd numbers :-
A number not divisible by 2 is called an odd number.
Example:- 1, 3, 5, 7, - - - - - -

Composite Numbers :-
Numbers greater than 1 which are not prime, are called composite numbers.
Example:- 4, 6, 8, 9, 10, - - - -. 6 -> 1,2,3,6.

Prime Numbers:-
A number greater than 1 having exactly two factors, namely 1 and itself is called a prime number. Upto 100 prime numbers are:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 71, 73, 79, 83, 89, 97

Co-prime Numbers:-
Two natural numbers a and b are said to be co-prime if their HCF is 1.
Example:- (21, 44), (4, 9), (2, 3), - - - - -

Twin prime numbers :-
A pair of prime numbers (as 3 and 5 or 11 and 13) differing by two are
called twin prime number.
Example:- The twin pair primes between 1 and 100 are
(3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), (71, 73).

Face value:-
Face value is the actual value of the digit.
Example:- In the number 7635, the "7" has a face value of 7, the face value of 3 is 3 and so on

Place value:-
The value of where the digit is in the number, such as units, tens, hundreds, etc.
Example:- In 352, the place value of the 5 is "tens"
Place value of 2 * 1 = 2;
Place value of 5 * 10 = 50;
Place value of 3 * 100 = 300.

1.

What is the place value of 7 in the numeral 2734?

A.) 70
B.) 7
C.) 700
D.) 7.00

7 × 100 = 700

2.

What is the place value of 3 in the numeral 3259

A.) 300
B.) 30
C.) 3
D.) 3000

3 × 1000 = 3000

3.

What is the diffference between the place value of 2 in the numeral 7229?

A.) 20
B.) 200
C.) 180
D.) 18

200 - 20 = 180

4.

What is the place value of 0 in the numeral 2074?

A.) 100
B.) 70
C.) 7.0
D.) 0

Note : The place value of zero (0) is always 0. It may hold any place in a number,
its value is always 0.

5.

What is the diffference between the place value and face value of 3 in the numeral 1375?

A.) 300
B.) 3
C.) 297
D.) 303

place value of 3 = 3 × 100 = 300
face value of 3 = 3
300 - 3 = 297

6.

A number when divided by a divisor leaves a remainder of 24.
When twice the original number is divided by the same divisor, the remainder is 11. What is the value of the divisor?

A.) 73
B.) 37
C.) 64
D.) 53

Let the original number be 'a'
Let the divisor be 'd'
Let the quotient of the division of aa by dd be 'x'
Therefore, we can write the relation as a/d = x and the remainder is 24.
i.e., a=dx+24 When twice the original number is divided by d, 2a is divided by d.
We know that a=dx+24. Therefore, 2a = 2dx + 48
The problem states that (2dx+48)/d leaves a remainder of 11.
2dx2dx is perfectly divisible by d and will therefore, not leave a remainder.
The remainder of 11 was obtained by dividing 48 by d.
When 48 is divided by 37, the remainder that one will obtain is 11.
Hence, the divisor is 37.

7.

The largest number amongst the following that will perfectly divide 101100 – 1 is:

A.) 100
B.) 10000
C.) 100^100
D.) 10

The easiest way to solve such problems for objective exam purposes is trial and error or by back
substituting answers in the choices given.
1012 = 10,201
1012 − 1 = 10,200.
This is divisible by 100.
Similarly try for 1013 − 1 = 1,030,301−1 = 1,030,300.
So you can safely conclude that (1011 − 1) to (1019 − 1) will be divisible by 100.
(10110 − 1) to (10199 − 1) will be divisible by 1000.
Therefore, (101100 − 1) will be divisible by 10,000.

8.

In an election, candidate A got 75% of the total valid votes. If 15% of the total votes were declared invalid and the total numbers of votes is 560000, find the number of valid vote polled in favour of candidate.

A.) 357600
B.) 356000
C.) 367000
D.) 357000

Total number of invalid votes = 15 % of 560000
= 15/100 × 560000
= 8400000/100
= 84000
Total number of valid votes 560000 – 84000 = 476000
Percentage of votes polled in favour of candidate A = 75 %
Therefore, the number of valid votes polled in favour of candidate A = 75 % of 476000
= 75/100 × 476000
= 35700000/100
= 357000

9.

Aravind had \$ 2100 left after spending 30 % of the money he took for shopping. How much money did he take along with him?

A.) \$ 3600
B.) \$ 3300
C.) \$ 3000
D.) \$ 3100

Let the money he took for shopping be m.
Money he spent = 30 % of m
= 30/100 × m
= 3/10 m
Money left with him = m – 3/10 m = (10m – 3m)/10 = 7m/10
But money left with him = \$ 2100
Therefore 7m/10 = \$ 2100
m = \$ 2100× 10/7
m = \$ 21000/7
m = \$ 3000
Therefore, the money he took for shopping is \$ 3000.

10.

A shopkeeper bought 600 oranges and 400 bananas. He found 15% of oranges and 8% of bananas were rotten. Find the percentage of fruits in good condition.

A.) 87.8%
B.) 86.8%
C.) 85.8%
D.) 84.8%

Total number of fruits shopkeeper bought = 600 + 400 = 1000
Number of rotten oranges = 15% of 600
= 15/100 × 600 = 9000/100 = 90
Number of rotten bananas = 8% of 400
= 8/100 × 400 = 3200/100 =32
Therefore, total number of rotten fruits = 90 + 32 = 122
Therefore Number of fruits in good condition = 1000 - 122 = 878
Therefore Percentage of fruits in good condition = (878/1000 × 100)%
= (87800/1000)% = 87.8%

• Division Algorithm:- If we divide a number by another number, then
Dividend = (Divisor * Quotient) + Remainder
D = d * Q + R
Example :- 7 = 3 * 2 + 1

Divisibility Rules

Divisibility by 2:-
The last digit of the given number should be 'zero' or 'even'
Example:- 12, 2498760, 34562, 745974 is divisible by 2.

Divisibility by 3:-
The sum of the digits of the number should be divisible by 3.
Example:- 1.) 123 => 1 + 2 + 3 = 6 = 6/3 = 2
Example:- 2.) 72954 => 7 + 2 + 9 + 5 + 4 = 27/3 = 9

Divisibility by 4:-
The last two digit of the given number should be 'zero' or 'divisible by 4.
Example:- 1.) 65837348 is divisible by 4, last two digits 48 is divisible by 4
Example:- 2.) 09214900 is divisible by 4, last two digits 00.

Divisibility by 5:-
The last digit of the given number should be 'zero' or '5'.
Example:- 1.) 8421745 is divisible by 5,
Example:- 2.) 9497440 is divisible by 5.

Divisibility by 6:-
The given number should be divisible by both 2 and 3.
Example:- 1.) 47562 is divisible by 2 as well as 3. so it is divisible by 6.
Example:- 2.) 59676 is divisible by 2 as well as 3. so it is divisible by 6.

Divisibility by 8:-
The last three digit of the given number should be 'zero' or 'divisible by 8.
Example:- 1.) 5478924568 is divisible by 8, last three digits 568 is divisible by 8
Example:- 2.) 69214000 is divisible by 8, last two digits 000.

Divisibility by 9:-
The sum of the digits of the number should be divisible by 9.
Example:- 1.) 786546 => 7 + 8 + 6 + 5 + 4 + 6 = 36 = 36/9 = 4
Example:- 2.) 72 => 7 + 2 = 9/9 = 1

Divisibility by 11:-
A number is divisible by 11, if the difference of the sum of its digits at odd places
and the sum of its digits at even places is either 0 or a nmber divisible by 11.
Example:- 1331, 14641, 123123, 9141.

11.

On dividinng 109 by a number, the quotient is 9 and the remainder is 1. Find the divisor.

A.) 13
B.) 12
C.) 14
D.) 11

d = (D-R)/Q
= (109 - 1)/9
= 108/9 = 12

12.

What is the dividend. divisor 17, the quotient is 9 and the remainder is 5.

A.) 153
B.) 156
C.) 158
D.) None of these

D = d × Q + R
D = 17 × 9 + 5
= 153 + 5
D = 158

13.

In a division sum, the divisor is ten times the quotient and five times the remainder. If the remainder is 46, the dividend is:

A.) 5336
B.) 5347
C.) 5337
D.) None of these

Divisor = (5 × 46) = 230
= 10 × Quotient = Divisor
=> Quotient = 230/10 = 23
Dividend = (Divisor × Quotient) + Remainder
Dividend = (230 × 23) + 46 = 5336

14.

In a division sum, the remainder is 6 and the divisor is 5 times the quotient and is obtained by adding 2 to the thrice of the remainder. The dividend is:

A.) 89
B.) 88
C.) 86
D.) 85

Divisor = (6 × 3) + 2 = 20
5 × Quotient = 20
Quotient = 4.
Dividend = (Divisor × Quotient) + Remainder
Dividend = (20 × 4) + 6 = 86

15.

In a question on division with zero remainder, a candidate took 12 as divisor instead of 21. The quotient obtained by him was 35. The correct quotient is:

A.) 26
B.) 25
C.) 0
D.) 20

Number = (35 × 12) = 420
Correct quotient = 420/21 = 20

16.

How many numbers from 10 to 50 are exactly divisible by 3.

A.) 13
B.) 12
C.) 14
D.) 11

12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45,48.
13 Numbers.
10/3 = 3 and 50/3 = 16 ==> 16 - 3 = 13. Therefore 13 digits.

17.

How many numbers from 10 to 100 are exactly divisible by 9.

A.) 8
B.) 11
C.) 10
D.) None of these

10/9 = 1 and 100/9 = 11 ==> 11 - 1 = 10. Therefore 10 digits.

18.

How many numbers from 29 to 79 are exactly divisible by 11.

A.) 5
B.) 6
C.) 4
D.) 7

29/11 = 2 and 79/11 = 7 ==> 7 - 2 = 5 Numbers

19.

How many numbers from 2 to 7 are exactly divisible by 2.

A.) 4
B.) 3
C.) 5
D.) None of these

3 - 1 = 2
2 + 1 = 3 Numbers.

20.

How many numbers from 10 to 100 are exactly divisible by 10.

A.) 12
B.) 11
C.) 9
D.) 10

10/10 = 1 and 100/10 = 10
==> 10 - 1 = 9
==> 9 + 1 = 10 Numbers

• Formulae:-
The sum of first n natural numbers is = [n(n+1)]/2.
Example:- 1.) The sum first 10 natural number is = [10(10+1)]/2 = [10(11)]/2 = 55
Example:- 2.) The sum first 49 natural number is = [49(49+1)]/2 = [49(50)]/2 = 49 * 25 = 1225

The sum of the squares of the first n natural numbers is = [n(n+1)(2n+1)]/6.
Example:- 1.) The sum of the squares of the first 10 natural numbers is = 10(11)(21)/6 = 385.

The sum of the cubes of the first n natural numbers is = [n(n+1)/2]2
Example:- 1.) The sum of the cubes of the first 10 natural numbers is = [10(10+1)/2]2

= [(10*11)/2]2 = 552 = 3025

The sum of the first n odd natural numbers is = n2
Example:- 1.) The sum of the first 24 odd natural numbers is = 242 = 576.
Example:- 2.) The sum of the first 9 odd natural numbers is = 92 = 81.

The sum of the first n even natural numbers is = n(n+1)
Example:- 1.) The sum of the first 10 even natural numbers is = 10(10 + 1) = 10 * 11 = 110
Example:- 2.) The sum of the first 12 even natural numbers is = 12(12 + 1) = 12 * 13 = 156

21.

How many numbers from 22 to 90 are exactly divisible by 11.

A.) 6
B.) 7
C.) 8
D.) 9

22/11 = 2 and 90/11 = 8
==> 8 - 2 = 6
==> 6 + 1 = 7 Numbers

22.

If a worker in a factory receives one rupee on the first day from the second days onwards his wage is increased by one rupee every day. What is the total amount of wage he receives after 40 days?

A.) Rs.720/-
B.) Rs.820/-
C.) Rs.810/-
D.) Rs.740/-

sum of n natural number = n(n+1)/2
= 40(41)/2
= Rs.820/-

23.

A bell in a clock rings once at 1 O'clock, twice at 2 O'clock, thrice at 3 O'clock and so on.. Then how many times it rings in a day.

A.) 150
B.) 146
C.) 136
D.) 156

sum of n natural number = n(n+1)/2
= 12(13)/2 = 78
= 2 times (78) = 156

24.

What is the sum of natural numbers between 20 and 100.

A.) 4860
B.) 4840
C.) 4880
D.) None of these

a = first number
l = last number
Sn = n/2[a + l]
between 20 and 100 numbers = 81 => 100 - 20 = 80 + 1 = 81
Sn = 81/2 × 120 = 81 × 60 = 4860

25.

What is the sum of all two digit numbers?

A.) 4900
B.) 4895
C.) 4905
D.) None of these

10 + 11 + 12 + 13 + 14 + 15 + - - - - - - - - + 97 + 98 + 99 + 100
Sn = n/2[a + l]
= 90/2[10 + 99]
= 45[109]
= 4905.

26.

What is the sum of all three digit numbers?

A.) 49550
B.) 49455
C.) 494450
D.) 494550

Sn = n/2[a + l]
= 900/2 [100 + 999]
= 450[1099]
= 494550

27.

If 123x4 is divisible by 4, then the digit in place of x is :

A.) 1
B.) 3
C.) 0
D.) 7

12314 is not divisible by 4
12334 is not divisible by 4
12304 is divisible by 4.

28.

If 32165* is divisible by 9, then the digit in place of * is :

A.) 9
B.) 1
C.) 0
D.) 2

321659 = 3 + 2 + 1 + 6 + 5 + 9 = 26 is not divisible by 9
321651 = 3 + 2 + 1 + 6 + 5 + 1 = 18 is divisible by 9.

29.

If 17617* is divisible by 11, then the digit in place of * is :

A.) 1
B.) 3
C.) 5
D.) 6

1 + 6 + 7 = 14
7 + 1 + 6 = 14.

30.

If 123xy is divisible by 40, then the value in place of x+y is :

A.) 1
B.) 7
C.) 4
D.) 3

123xy
1 + 0 = 1/4 ≠ 40
7 + 0 = 70/4 ≠ 40
4 + 0 = 40/4 = 10

31.

Which of the following numbers is not divisible by 3?

A.) 123
B.) 1234
C.) 12345
D.) 123456

1 + 2 + 3 = 6/3 = 2 is divisible by 3
1 + 2 + 3 + 4 = 10/3 ≠ 3 is not divisible by 3

32.

Find the unit digit in the product (243 × 397 × 2497 × 3913)?

A.) 4
B.) 2
C.) 1
D.) 3

3 × 7 × 7 × 3 = 441
Reruired digit = 1

33.

What is tha value of (x-a)(x-b)(x-c) - - - - - (x-z)

A.) 1
B.) 2
C.) 3
D.) 0

(x-a)(x-b)(x-c)- - - - (x-x)(x-y)(x-z)
here, x-x = 0.

34.

What is the unit digit in 29

A.) 3
B.) 4
C.) 1
D.) 2

Cyclicity of 2 = 4
21 = 2
22 = 4
23 = 8
24 = 16 means unit place is 6
25 = 32 means unit place is 2, 4, 8, 6, 2, 4, 8, 6, 2,- - - - -
9/4 = Remainder 1, 21 = 2
Here 1 is remainder
Note:-
Cyclicity of 2, 3, 7, 8 => 4
Cyclicity of 4, 9 => 2
Cyclicity of 1, 5, 6 => 1

35.

What is the unit digit in 230?

A.) 3
B.) 4
C.) 1
D.) 2

Cyclicity of 2 = 4
D = d × Q + R
30 = 4 × 7 + 2
30/4 = Remainder 2, 22 = 4
Note:-
Cyclicity of 2, 3, 7, 8 => 4
Cyclicity of 4, 9 => 2
Cyclicity of 1, 5, 6 => 1

36.

What is the unit digit in 337?

A.) 3
B.) 5
C.) 7
D.) 9

Cyclicity of 3 also = 4
D = d × Q + R
37 = 4 × 9 + 1
37/4 = Remainder 1, 31 = 3
Note:-
Cyclicity of 2, 3, 7, 8 => 4
Cyclicity of 4, 9 => 2
Cyclicity of 1, 5, 6 => 1

37.

The LCM of two numbers is 280 and their ratio is 7 : 8. The two numbers are

A.) 36, 40
B.) 80, 90
C.) 43, 49
D.) 35, 40

Let the number be 7x and 8x
HCF = x
We know HCF × LCM = product of two numbers
HCF × LCM = 7x × 8x
280x = 56x2
x = 5
Thus, numbers are 35 and 40

38.

The least number which should be added to 2497 so that the is exactly divisible by 5, 6, 4 and 3 is

A.) 25
B.) 23
C.) 27
D.) 29

L.C.M of 3, 4, 5 and 6 is 60
2520 is divisible by 60

39.

Four prime numbers are written in ascending order. The product of the first 3 numbers is 105. The product of the last 3 is 385. Find the second number

A.) 7
B.) 9
C.) 5
D.) 25

Let the numbers a, b, c and d.
abc = 105
bcd = 385
HCF(abc, bcd) = bc
Since a and d are prime.
105 = 3 × 5 × 7
385 = 5 × 7 × 11
HCF(105, 385) = 35 = 5 × 7
The second number is 5.

40.

Which of the following numbers is divisible by 6?
(i) 5647386  (ii) 8460398 (iii) 2385972

A.) (i) and (ii) only
B.) (ii) and (iii) only
C.) (i) and (iii) only
D.) (i) only

For a number to be divisible by 6,
It should be divisible by both 2 and 3
1.) 5,64,386
Test for divisibility by 3
5 + 6 + 4 + 3 + 8 + 6 = 39
39 is divisible by 3.
2.) Test for divisibility by 2
The last digit of 5,647,386 is 6
The number is even
Therefore, 5,647,386 is divisible by two.

8,460,398

Test for divisibility by 3
8 + 4 + 6 + 0 + 3 + 9 + 8 = 38
38 is divisible by 3.
2.) Test for divisibility by 2
The last digit of 8,460,398  is 8
The number is even
Therefore, 8,460,398 is divisible by two.

41.

68n - 58n, where n>0 is an integer, is divisible by

A.) 6
B.) 671
C.) 21
D.) 39

For n = 1,
68 - 5 8 = (64)2 - (54)2 = (64 + 54)(64 - 54)
= (1921) (671)

42.

6/7 of a certain number is 96. Find quarter of that number.

A.) 112
B.) 23
C.) 32
D.) 28

6/7x = 96
x = 112
y = x/4 = 112/4 = 28

43.

Find the HCF of 59 , 14?

A.) 826
B.) 1
C.) 2
D.) 3

The fastest way to find the correct answer is by elimination rule :
Check whether each of the given choices divides both the numbers. If any of the given choices doesnâ€™t divide both the numbers, then you can eliminate that particular choice and move to the next choice. Answer will be the HIGHEST Number that exactly divides both given numbers.
Please Note : There may be a scenario when two or more numbers in the choice will exactly divide both the numbers, in that case , please choose the Highest among the numbers.

44.

Two people run around circular track and take 42 sec and 30 sec to make one complete round. If they start together after how much amount of time will they meet again in the same place?

A.) 3 min 30 sec
B.) 4 min 40 sec
C.) 3 min 20 sec
D.) 2 min 50 sec

LCM ( 42, 30) = 210
They will meet in 210 seconds, which is 3 min 30 sec.

45.

What number should come next ?
173, 196, 219, 242, _____

A.) 265
B.) 267
C.) 263
D.) 264

The given series is -- 173, 196, 219, 242
Consequtive numbers increases by 23
Following this pattern, the Missing Number should increase by 23 from the previous number.
When we add 23 to the last number (i.e 242) we get 242+23=265

46.

What should come in place of _____ in the below number series?
173, 149, 125, 101, _____

A.) 76
B.) 77
C.) 78
D.) 79

The given series is -- 173, 149, 125, 101
Consequtive numbers decreases by 24
Following this pattern, the Missing Number should decrease by 24 from the previous number.
When we subract 24 to the last number (i.e 101) we get 101- 24 = 77

47.

Find the HCF of 59 , 12?

A.) 1
B.) 2
C.) 3
D.) 708

The fastest way to find the correct answer is by elimination rule :
Check whether each of the given choices divides both the numbers. If any of the given choices doesnâ€™t divide both the numbers, then you can eliminate that particular choice and move to the next choice. Answer will be the HIGHEST Number that exactly divides both given numbers.
Please Note : There may be a scenario when two or more numbers in the choice will exactly divide both the numbers, in that case , please choose the Highest among the numbers.

48.

Find the LCM of 42 , 20?

A.) 504
B.) 360
C.) 1680
D.) 420

The fastest way to find the correct answer is by elimination rule :
Check whether each of the given choices is divisble by both the numbers. If any choice doesnâ€™t get divided by both the numbers, then you can eliminate that particular choice and move to the next number. Answer will be the Number that is exactly divisble by both given numbers.
Please Note : There may be a scenario when two or more numbers in the choice will be exactly divisible by both the numbers, in that case , please choose the lowest among the numbers.

49.

In the below given sequence, what should be the next number?
173, 195, 217, 239, _____

A.) 263
B.) 261
C.) 259
D.) 260

The given series is -- 173, 195, 217, 239
Consequtive numbers increases by 22
Following this pattern, the Missing Number should increase by 22 from the previous number.
When we add 22 to the last number (i.e 239) we get 239+22=261

50.

Output of a particular program follows the below pattern. Can you find the next number ?
173, 151, 129, 107, _____

A.) 84
B.) 83
C.) 87
D.) 85