Question

A man borrows 850 taka from bank. The bill is renewed after every half year at an increase of 21% . After how much time amount will become 8500 taka.

Answer 1

$FV=PV(1+i)^n$

where $FV$ is future value, $PV$ is present value, $i$ is the interest per compounding period, $n$ is the number of compounding periods.

$n=\frac{lnFV-lnPV}{ln(1+i)}$

$n=\frac{ln8500-ln850}{ln1.21}=12.08=6.04$ years