Question

the compound interest, compounded annually, on a certain sum is rupees 9680 in the 2nd year and is rupees 10648 in the third year calculate the rate of interest, the interest for the fourth year, the interest for the first year .

Answer 1

  let  r be rate of interest
(9680 x r x 1 ) / 100= 10648
  9680r/100=10648
9680r/100 x 100= 10648 x 100
9680r = 1064800
9680r / 9680 = 1064800/ 9680
r = 1064800/9680=106480/968= 110
so rate of interest = 110 

let p be interest of first year
Interest in second year= ( p x 110 x  1)/ 100
9680= 110p/100
9680x 100 = 110p/100 x 100
968000/110= 110p/110
880=  p
so interest of first year = 8800

let interest of fourth year be y
y= 10648 x 110 x 1/  100
y= 1812800/100
y = 18128

SO
Rate of Interest = 110%
Interest for First year= 8800
Interest for fourth year= 18128


 

Answer 2

let  r be rate of interest
(9680 x r x 1 ) / 100= 10648
  9680r/100=10648
9680r/100 x 100= 10648 x 100
9680r = 1064800
9680r / 9680 = 1064800/ 9680
r = 1064800/9680=106480/968= 110
so rate of interest = 110 

let p be interest of first year
Interest in second year= ( p x 110 x  1)/ 100
9680= 110p/100
9680x 100 = 110p/100 x 100
968000/110= 110p/110
880=  p
so interest of first year = 8800

let interest of fourth year be y
y= 10648 x 110 x 1/  100
y= 1812800/100
y = 18128

SO
Rate of Interest = 110%
Interest for First year= 8800
Interest for fourth year= 18128