RRB NTPC - Ratios and Proportions (114 Questions with Explanation)

1.

In a bag, there are coins of 25 p, 10 p and 5 p in the ratio of 1 : 2 : 3. If there is Rs. 30 in all, how many 5 p coins are there?

   A.) 50
   B.) 150
   C.) 100
   D.) 200

Answer: Option 'B'

Let the number of 25 p, 10 p and 5 p coins be x, 2x, 3x respectively.
Then, sum of their values = Rs. ( 25 x / 100 + 10 x 2x / 100 + 5 x 3x/ 100 ) = RS. 60x /100
Therefore, 60x/100 = 30 <=> x = 30 x 100/60 = 50
Hence, the number of 5 p coins = (3 x 50) = 150.

2.

If a dozen mirrors are fallen down. The ratio between broken and unbroken mirrors is: 

   A.) 2:3
   B.) 3:4
   C.) 5:7
   D.) 5:4

Answer: Option 'C'

Dozen means = 12 
12/(2+3) = 12/5 ==> wrong 
12/(3+4) = 12/7 ==> wrong 
12/(5+7) = 12/12 = 1 ==> Right (Answer = 5:7)

3.

If a:b=1:2, b:c=3:4 and c:d = 2:3 find a:b:c:d? 

   A.) 3:6:8:24
   B.) 6:12:16:24
   C.) 6:18:24:16
   D.) 3:6:2:3

Answer: Option 'B'

a:b = 1:2, b:c = 3:4, c:d = 2:3
1:2 
3:4 
( a = 1 × 3 = 3, b = 2 × 3 = 6 and c = 2 × 4 = 8)
(a = a × b, b= b × b and c= b × c) 
a:b:c = 3:6:8 
a:b:c = 3:6:8 and c:d = 2:3
(Note: First a,b,c multiplication with c means 2 and last c means 8
multiplication with d means 3
a:b:c:d = 6:12:16:24 

4.

20 boys and 25 girls form a group of social workers. During their membership drive, the equal number of boys and girls joined this group. How many members does the group have now, if the ratio of boys to girls is 7 : 8 ?

   A.) 75
   B.) 60
   C.) 65
   D.) 63

Answer: Option 'A'

Let x girls and x boys join this group.
Then (20+x) / (25+x) = 7/8 => 160 + 8x = 175 + 7x => x = 15
Boys = 20 + 15 = 35 Girls = 25 + 15 = 40, total = 35 + 40 = 75

5.

A sum of money is to be distributed among A, B, C, D in the proportion of 5 : 2 : 4 : 3. If C gets Rs. 1000 more than D, what is B's share?

   A.) Rs. 2000
   B.) Rs. 2500
   C.) Rs. 1500
   D.) Rs. 1000

Answer: Option 'A'

Let the shares of A, B, C and D be Rs. 5x, Rs. 2x, Rs. 4x and Rs. 3x respectively.
Then, if C gets Rs. 1000 more than D
=> 4x - 3x = 1000
=> x = 1000
B's share = Rs. 2x = Rs. (2 x 1000) = Rs. 2000
Answer is 2000

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