A person deposited Rs. 100 in a bank and gets the amount Rs. 121 after two years . The rate of the compound interest is _______ % . ( WBBSE – 2019 )

A person deposited ₹ 100 in a bank and gets the amount ₹ 121 after two years . The rate of the compound interest is ______% .

Answer : 10%

Explatation :

Principal (P) = ₹ 100

Amount (A) = ₹ 121

Time (T) = ??

According to problem,

A = P ( 100+R/100 )^T

⇒ 121 = 100 ( 100+R/100 )²

⇒ 121 = 100 × ( 100+R )² / 100 × 100

⇒ ( 100+R )² = 121 × 100

⇒ 100+R = √ ( 121 × 100 )

⇒ 100+R = √ ( 11×11×10×10 )

⇒ 100+R = 11×10

⇒ 100+R = 110

⇒ R = 110 – 100

⇒ R = 10

Required rate = 10%