The fourth proportional to 16, a and 9a is 324. What is the value of a?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 24
16 : a = 9a : 324
16 × 324 = a × 9a
5184 = 9a²
a² = 5184 ÷ 9 = 576
a = √576 = 24
∴ a = 24