A sum of Rs. 12,000.00 deposited at compound interest becomes double at the end of 5 years. At the end of 15 years the sum will be:

Question

Question

This question was previously asked in

NTPC CBT-I (Held On: 7 Jan 2021 Shift 1)

Answer 1

Given:

Principal = Rs.12000

Time = 5 years

Formulas used:

Amount = Principal × (1 + r/100)ⁿ

Calculation:

Amount = Principal × (1 + r/100)⁵

⇒ 24000 = 12000 × (1 + r/100)5

⇒ 24000/12000 = (1 + r/100)5

⇒ 2 = (1 + r/100)5 (1)

⇒ At the end of 15 years,

⇒ Amount = 12000 × (1 + r/100)¹⁵

⇒ Amount = 12000 × [(1 + r/100)⁵]³ (From 1)

⇒12000 × 2³

⇒12000 × 8

⇒ 96000

∴ The amount at the end of 15 years will be Rs.96000

Shortcut Trick F1 Ravi Ravi 17.11.21 D14

∴ The amount at the end of 15 years will be 8 times of 12000 = Rs.96000