Compound Interest :

1. Madan invested an amount of Rs. 30000 at compound interest rate 5% p.a. for a period of 2 years. What amount will he receive at the end of 2 years ?

Solution : Here, P = 30000, R = 5 and t = 2

∴ Amount = P(1+R/100)t

= 30000(1+5/100)² = 30000(1+1/20)²

= 30000×21×21/20×20 = Rs.33075

2. Find compound interest on Rs.10000 for 2 years at 4% p.a.

Solution : Here, P= 10000, R= 4 and t=2

∴ CI = P[(1 + R/100)t – 1 ]

= 10000[(1 + 4/100)² – 1 ]

=10000[(26/25)² – 1 ] = 10000((1.04)² − 1)

= 10000(1.0816 – 1) =Rs.816

∴ The compound interest is Rs. 816

3. Ragini invested Rs. 32000 for 2 years at compound interest and received an amount of Rs. 35280 on maturity. What is the rate of interest ?

Solution : Here, P= 32000, t= 2 and A = 35280

∴ R = 100[(A/P)1/t – 1 ]% p.a.

= 100[(35280/32000)1/₂ – 1 ]% p.a.

= 5% p.a

4. Find the amount of Rs. 16000 in 3/2 years at 5% per annum compound interest payable half-yearly.

Solution : Here, P =16000. R = 5 and t = 3/2

∴ Amount = P (1+R/100×2)2t

= 16000(1+5/100×2)2×3/2

= 16000(41/40)³

= 17230.25

5. Find the compound interest on Rs. 2000 at 40% per annum compounded quarterly for 1 year.

Solution : Here, P =2000. R = 40 and t = 1

∴Compound interest (CI)

= P[(1+ R/100×4)4×t − 1]

= 2000[(1+ 40/100×4)4×1 − 1]

= 2000[(11/10)4 − 1]

= 2000[14641−10000/10000]

= Rs.928.20