Question

At a certain rate of simple interest, a sum of $Rs.6400$ becomes $Rs.8000$ in $2$ years. What sum of money will become $Rs.15510$ in $3$ years at the same rate of interest?

Answer 1

Rate of interest is unknown. Let us assume it as r.

Amount invested $P=6400$

Amount received with interest $=8000$

Time $=2years$

Interest for $2$ years for $6400=8000-6400=1600$

Simple interest $=PTR\times \frac{1}{100}=6400\times 2\times r\frac{1}{100}=1600$

Simplify to get $r=12.5\%$

II Part:

Now rate of interest is known $=12.5$

P is not known.

Final amount $=15510$

$Tenure=3years$

Final amount = $P+(PTR\times \frac{1}{100})$= $15510$

$P\times (1+(3\times 12.5\frac{1}{100}))=15510$

Simplify to get

$P\times \left(1.375\right)$ =$15510$

$P=15510\times \frac{1}{1.375}=11280$ Rs