If a : b = 5 : 7, then (6a2 - 2b2) : (b2 - a2) will be:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 13 : 6.
a : b = 5 : 7 = 5x : 7x
⇒ (6a2 - 2b2) : (b2 - a2)
⇒ (6 × (5x)2 - 2 × (7x)2)/((7x)2 - (5x)2)
⇒ (6 × 25x2 - 2 × 49x2)/24x2
⇒ (150x2 - 98x2)/24x2
⇒ 52/24 = 13/6 = 13 : 6