CAT 2017 Slot 1 — QA Question 24
IndicesEasy
If 92x–1 – 81x-1 = 1944, then x is
Answer & solution
- A
3
9/4
- C
4/9
- D
1/3
Solution
92x–1 – 81x-1 = 1944
⇒ 92x–2 × 9 – 92x-2 = 1944
⇒ 92x–2 (9 – 1) = 8 × 243 = 8 × 35
⇒ 34x–4 × 8 = 8 × 35
⇒ ∴ 4x – 4 = 5
∴ x = 9/4.
Hence, option (b).