Question

Amar borrowed 800 rupees at a rate of 5% per annum.the ammount he will pay after 3 half years is

Answer 1

Should be posted in the Mathematics section, though I'll solve this.
Amount= Simple Interest (SI) + Principal (P)

P= Rs. 800
Rate of Interest (R)= 5%
Time(T)= 3 years 6 months = 3 1/2 years= 7/2 years 

SI= (P x R x T)/100
   = (800 x 5 x 7/2)/100 
SI= Rs. 1400

Amount= SI + P= 1400 + 800= Rs. 2200