Question

A sum becomes triple in $6$ years at S.I. The same sum will become $19$ times in how many years?

Answer 1

Let the sum be x

simple interest on x for 6 years= x (as the sum doubles)

$SI=\frac{PRT}{100}\Rightarrow x=\frac{xR\times b}{100}\Rightarrow R=\frac{100}{6}$

For the sum x to become 8 x, simple interest = 7x

$7x=\frac{xRT}{100}\Rightarrow 7=\frac{RT}{100}\Rightarrow 7=\frac{\frac{100}{6}\times T}{100}=\frac{T}{6}$

$\Rightarrow T=7\times 6=42$ years