Ex.8.3 Q10 Compairing Quantities - NCERT Maths Class 7

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Question

What rate gives \(\rm Rs \,280\) as interest on a sum of \(\rm Rs\, 56,000\) in \(2\) years?

Text Solution

What is Known?

Principal, interest and number of years. 

What is Unknown?

Rate of interest.

Reasoning:

Rate of Interest can be calculated using the formula

Simple Interest  

\[\begin{align} & =\frac{\left[ \begin{align} & \text{Principal} \times  \text{Rate of interest} \\ &  \times  \text{Time (in years)} \\ \end{align} \right]}{100} \\ \end{align}\]

Steps:

Let us assume that rate of interest to be \(\rm{R.}\)

So, Simple Interest 

\[\begin{align}{\rm{ = }}\,\frac{{{\rm{Principal}}\,{\rm{ \times Rate}}\,{\rm{ \times }}\,{\rm{Time}}}}{{{\rm{100}}}}\end{align}\]

\[\begin{align}{\rm{I}}{\rm{.E}\,}{\rm{.\,280}}\, &=\frac{{{\rm{56000}} \times {\rm{R}}\, \times {\rm{2}}}}{{{\rm{100}}}}\\{\rm{R}} &= \frac{{280 \times 100}}{{56000 \times 2}}\\ &= 0.25\%\end{align}\]

So, the rate of interest is \(0.25\%\)