Question

A certain sum amounts to Rs. 798.60 after 3 years and Rs. 878.46 after 4 years. Find the interest rate and the sum.
a) 7.5% , Rs. 300
b) 5% , Rs. 550
c) 9% , Rs. 450
d) 10% , Rs. 600
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Answer 1

Answer:

It is given that

Amount after 3 years = 798.60

Amount after 4 years = 878.46

So the difference = 878.46 - 798.60 = 79.86

Here 79.86 is the interest of 798.60 for 1 year.

We know that

Rate = (SI×100)/(P×t)

Substituting the values

=(79.86×100)/(798.60×1)

Multiply and divide by 100

=(7986×100×100)/(79860×100×1)

=10%

Here

A= P(1+r/100)

n

It can be written as

P=A÷(1+r/100)

n

Substituting the values

P= 798.60÷(1+10/100)

3

By further calculation

P=79860/100×10/11×10/11×10/11

P=600

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