We can use the formula for compound interest to solve the problem:
A = P(1 + r/n)^(nt)
Where:
A = final amount (17280)
P = principal amount (10000)
r = annual interest rate (to be found)
n = number of times interest is compounded per year (assuming it is compounded annually, n = 1)
t = time period in years (3)
Substituting the given values and solving for r:
17280 = 10000(1 + r/1)^(1*3)
17280/10000 = (1 + r)^3
cbrt(1728/1000) = 1 + r
r = cbrt(1728/1000) - 1
r = 0.08 or 8%
Therefore, the annual interest rate is 8%.
#10000 invested for 3 years at r% per annum compound interest amount to #17280. Find r
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