If (10a3 + 4b3) : (11a3 - 15b3) = 7 : 5, then (3a + 5b) : (9a - 2b) = ?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 10 : 13
Concept
Ratio and cross multiplication
Application
(10a3 + 4b3) : (11a3 - 15b3) = 7 : 5
Cross Multiplying
5 × (10a3 + 4b3) = 7 × (11a3 - 15b3)
50a3 + 20b3 = 77a3 - 105b3
27a3 = 125b3
3a = 5b
a : b = 5 : 3
Putting the values of a and b in (3a + 5b) : (9a - 2b)
( 3 x 5 + 5 x 3) : ( 9 x 5 - 2 x 3)
= 30 : 39
= 10 : 13