A sum of ₹1200 is invested at compound interest (compounded half yearly). If the rate of interest is 10% per annum, then what will be the amount after 18 months?

₹1389.15

For 1/3rd year ,

Rate of interest = \(\frac{10}{2}\)% = 5%

18 months = 3 half year

From the formula for compound interest, we know,

C.I = P(1+$\frac{R}{100})^t$– P

 = 1200 [ 1 + \(\frac{5}{100}\) ]³ - 1200

 = 1200 [ \(\frac{21}{20}\) × \(\frac{21}{20}\) × \(\frac{21}{20}\) - 1 ]

 = 1200[ \(\frac{  9261 }{8000}\)  - 1 ]

= 1200 [ \(\frac{1261}{8000}\) ]

= 189.15

So, Amount after 18 months = 1200 + 189.15

= Rs. 1389.15