If x is the mean proportional between 12.8 and 64.8 and y is the third proportional to 38.4 and 57.6, then 2x : y is equal to:
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e 2 : 3
| Understanding | Application |
|
Mean proportional of two numbers a & b is x if a / x = x / b. |
a = 12.8 b = 64.8 ⇒ a / x = x / b ⇒ x2 = ab ⇒ x2 = 829.44 ⇒ x = 28.8 |
| The third proportion will be y of twonumbers p & q when, p : q :: q : y. |
p = 38.4 q = 57.6 ⇒ p / q = q / y ⇒ y = q2 / p ⇒ y = 3317.76 / 38.4 ⇒ y = 86.4 ⇒ 2x : y ⇒ 2(28.8) : 86.4 ⇒ 2 : 3 |