# Ex.8.3 Q9 Compairing Quantities - NCERT Maths Class 7

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## Question

Find the amount to be paid at the end of $$3$$ years in each case:

(a)  Principal $$= \rm Rs\, 1,200$$ at $$12\%$$ p.a.

(b) Principal $$= \rm Rs\, 7,500$$ at $$5\%$$ p.a.

Video Solution
Comparing Quantities
Ex 8.3 | Question 9

## Text Solution

What is Known?

Principal, Time and the rate of interest.

What is Unknown?

Amount to be paid in three years.

Reasoning:

Simple 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]}{\text{100}\ } \\ \end{align}

And amount is obtained by adding Principal to the interest

Steps:

(a) Principal = $$\rm Rs\, 1,200$$ at $$12\%$$ p.a.

Simple Interest

\begin{align} & =\frac{\left[ \begin{align} & \text{Princial} \times \text{Rate of interest} \\ & \times \text{Time (in years)} \\ \end{align} \right]}{100} \\ & =\frac{1200 \times 12 \times 3}{100} \\ & =\text{Rs }432 \\ \end{align}

\begin{align}\text{Amount} &=\text{Principal + Interest }\\&= \text{Rs }1200 + \text{Rs }432 \\ &= \text{Rs }1632\end{align}

So, the amount to be paid after $$3$$ years will be $$\rm Rs. \,1632$$

(b) Principal $$= \rm Rs \,7,500$$ at $$5\%$$ p.a.

Simple Interest

\begin{align}& =\frac{\left[ \begin{align} & \text{Princial} \times \text{Rate of interest} \\& \times \text{Time (in years)} \\ \end{align} \right]}{100} \\ & =\frac{7500 \times 5 \times 3}{100} \\ & =1125 \end{align}

\begin{align}\text{Amount} &= \text{Principal + Interest}\\&= 7500 +1125 \\&= 8625\end{align}

So, the amount to be paid after $$3$$ years will be $$\rm Rs.\,8625$$

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