A sum of money becomes eight times of itself in 3 years at compound interest. The rate of interest per annum is
Options:
A . 10%
B . 100%
C . 20%
D . 80%
Answer: Option B Answer: (b)Let the principal be x and the rate of compound interest be r% per annum. Then,$8x = x(1 + r/100)^3$8 = $(1 + r/100)^3$$2^3 = (1 + r/100)^3$2 = $1 + r/100 ⇒ r/100 = 1 ⇒ r = 100%$Using Rule 8,If a sum becomes 'n' times of itself in 't' years on compound interest, then R% = $[n^{1/t} - 1] × 100%$
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