Question

a sum of money to 780 in two years and 1230 in seven years .find principal and rate of simple intrest

Answer 1

let P is the principal and r is the rate of SI

use formula ,
SI=P x r x t/100
(780 - P) =P x r x 2 /100 -------------(1)

again ,

(1230 - P) = P x r x 7/100 ------------(2)

divide equation (1) and (2)

(780 - P)/(1230 - P) = 2/7

7 (780 - P) = 2 (1230 - P)

5460 - 7P = 2460 - 2P

3000 = 5P

P = 600 Rs
hence principal is 600 Rs
now put P =600 in equation (1)

780-600= 600 x r x 2/100
180 = 12 r
r =15 %

hence rate of simple interest is 15 %

Answer 2

HI Friend,

Let the amount be Rs x and rate of interest is r%

then (x+x*r*2/100) = 780....(1)

and x+x*r*7/100 = 1230...(2)

subtracting 2 from 1

then 5xr/100 = 450

or, xr = 9000

then x+180=780

hence pricipal amount is Rs 600 and rate of interest is15% .

Wish it helps ^_^