Aptitude - Ratio and Proportion
1.
If A : B = 5 : 7 and B : C = 6 : 11, then A : B : C = ?
Answer
A : B = 5 : 7 = 30 : 42 and B : C = 6 : 11 = 42 : 77
⇒ A : B : C = 30 : 42 : 77
Answer :
Option BExplanation :
A : B = 5 : 7 = 30 : 42 and B : C = 6 : 11 = 42 : 77
⇒ A : B : C = 30 : 42 : 77
2.
Two whole numbers whose sum is 64, cannot be in the ratio
Answer
For dividing 64 into two whole numbers, the sum of the terms of the ratio must be a factor of 64.
So, they cannot be in the ratio 3 : 4
Answer :
Option CExplanation :
For dividing 64 into two whole numbers, the sum of the terms of the ratio must be a factor of 64.
So, they cannot be in the ratio 3 : 4
3.
Fourth proportional to 0.2, 0.12 and 0.3 is :
Answer
Let the required number be x. Then,
0.2 : 0.12 = 0.3 : x ⇒ 0.2x = 0.12 x 0.3
⇒ x = 362 x 100 = 0.18
Answer :
Option CExplanation :
Let the required number be x. Then,
0.2 : 0.12 = 0.3 : x ⇒ 0.2x = 0.12 x 0.3
⇒ x = 362 x 100 = 0.18
4.
What should be subtracted from each of the numbers 54, 71, 75, 99 so that the remainders may be proportional ?
Answer
Let the number to be subtracted be x. Then,
54 − x71 − x = 75 − x99 − x ⇒ (54 − x)(99 − x) = (75 − x)(71 − x)
⇒ 5346 − 153x + x2 = 5325 − 146x + x2
⇒ 7x = 21 ⇒ x = 3
∴ The required number is 3.
Answer :
Option CExplanation :
Let the number to be subtracted be x. Then,
54 − x71 − x = 75 − x99 − x ⇒ (54 − x)(99 − x) = (75 − x)(71 − x)
⇒ 5346 − 153x + x2 = 5325 − 146x + x2
⇒ 7x = 21 ⇒ x = 3
∴ The required number is 3.
5.
In a school, the ratio of boys and girls is 4 : 5. When 100 girls leave the school, the ratio becomes 6 : 7. How many boys are there in the school ?
Answer
Let the number of boys and girls be 4x and 5x respectively. Then,
4x5x − 100 = 67 ⇒ 28x = 30x − 600
⇒ 2x = 600 ⇒ x = 300
Number of boys = (4 x 300) = 1200
Answer :
Option DExplanation :
Let the number of boys and girls be 4x and 5x respectively. Then,
4x5x − 100 = 67 ⇒ 28x = 30x − 600
⇒ 2x = 600 ⇒ x = 300
Number of boys = (4 x 300) = 1200
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