Number System : Aptitude Test (200 Questions with Explanation)

1.

Which one of the following is not a prime number?

   A.) 31
   B.) 91
   C.) 61
   D.) 71

Answer: Option 'B'

91 is divisible by 7. So, it is not a prime number.

2.

What least number must be added to 1056, so that the sum is completely divisible by 23 ?

   A.) 2
   B.) 3
   C.) 18
   D.) 21

Answer: Option 'A'

23) 1056 (45 92 --- 136 115 --- 21 --- 
Required number = (23 - 21) = 2.

3.

666 x 6{-1} x 3{-1} = ?

   A.) 37
   B.) 333
   C.) 111
   D.) 84

Answer: Option 'A'

Given Exp. = 666 x 1/6 x 1/3 = 37

4.

The sum of first five prime numbers is:

   A.) 11
   B.) 18
   C.) 26
   D.) 28

Answer: Option 'D'

Required sum = (2 + 3 + 5 + 7 + 11) = 28. Note: 1 is not a prime number. (Definition: A prime number (or a prime) is a natural number that has exactly two distinct natural number divisors: 1 and itself.)

5.

( 112 x 54) = ?

   A.) 67000
   B.) 70000
   C.) 76500
   D.) 77200

Answer: Option 'B'

(112 x 54) = 112 x ( 10/2 )4 = 112 x 104 / 24 = 1120000 / 16 = 70000

6.

A boy multiplied 987 by a certain number and obtained 559981 as his answer. If in the answer both 9 are wrong and the other digits are correct, then the correct answer would be:

   A.) 555681
   B.) 553681
   C.) 555181
   D.) 556581

Answer: Option 'A'

987 = 3 x 7 x 47 So, the required number must be divisible by each one of 3, 7, 47 553681 (Sum of digits = 28, not divisible by 3) 555181 (Sum of digits = 25, not divisible by 3) 555681 is divisible by 3, 7, 47.

7.

Find the HCF of 59 , 14?

   A.) 826
   B.) 1
   C.) 2
   D.) 3

Answer: Option 'A'

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 doesn’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.

8.

Find a positive number which when increased by 17 is equal to 60 times the reciprocal of the number .

   A.) 3
   B.) 10
   C.) 17
   D.) 20

Answer: Option 'A'

Let the number be x.
Then, x + 17 = 60 / x
=> x2 + 17x - 60 = 0
=> (x + 20)(x - 3) = 0
=> x = 3.

9.

In the given series, can you find the Missing number ?
117, 94, 71, X , 25, 2

   A.) 47
   B.) 46
   C.) 50
   D.) 48

Answer: Option 'D'

The given series is -- 117, 94, 71, X , 25, 2
Consequtive numbers decreases by 23
Following this pattern, the Missing Number X should decrease by 23 from the previous number.
When we subract 23 to the number before X (i.e 71) we get 71--23=48

10.

Fourth number is missing in the below series. Can you find the Fourth number in the below series ?
117, 140, 163, X , 209, 232

   A.) 185
   B.) 184
   C.) 186
   D.) 188

Answer: Option 'C'

The given series is -- 117, 140, 163, X , 209, 232
Consequtive numbers increases by 23
Following this pattern, the Missing Number X should increase by 23 from the previous number.
When we add 23 to the number before X (i.e 163) we get 163+23=186

11.

Find the LCM of 25 , 3?

   A.) 75
   B.) 150
   C.) 48
   D.) 100

Answer: Option 'A'

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 doesn’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.

12.

A number consists of two digits. If the digits interchange places and the new number is added to the original number, then the resulting number will be divisible by:

   A.) 3
   B.) 5
   C.) 7
   D.) 11

Answer: Option 'D'

Let the ten's digit be x and unit's digit be y. Then, number = 10x + y. Number obtained by interchanging the digits = 10y + x. Therefore, (10x + y) + (10y + x) = 11(x + y), which is divisible by 11.

13.

What is the sum of all three digit numbers? 

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

Answer: Option 'D'

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

14.

(xn - an) is completely divisible by (x - a),when

   A.) n is any natural number
   B.) n is an even natural number
   C.) n is an odd natural number
   D.) n is prime

Answer: Option 'A'

For every natural number n, (x^n - a^n) is completely divisible by (x - a).

15.

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

Answer: Option 'D'

The given series is -- 173, 151, 129, 107
Consequtive numbers decreases by 22
Following this pattern, the Missing Number should decrease by 22 from the previous number.
When we subract 22 to the last number (i.e 107) we get 107-22 = 85

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