A principal gets increased by 21% in 2 years at compound interest. What will be the simple interest on ₹1000 for 4 years at the same rate of interest?

₹400

Compound interest for 2 years = 21%

Amount = Principal × ( 1 + \(\frac{R }{100}\) )^t

Let principal = 100

So , 121 = 100 × ( 1 + \(\frac{R }{100}\) )²

\(\frac{121 }{100}\) = ( 1 + \(\frac{R }{100}\) )²

\(\frac{11 }{10}\) = ( 1 + \(\frac{R }{100}\) )

\(\frac{R }{100}\) = \(\frac{1 }{10}\)

R = 10%

Now , Simple Interest = \(\frac{Principal ×Rate × Time }{100}\)

= \(\frac{1000 × 10× 4 }{100}\)

= Rs. 400