CBSE Class 8 Answered

1)A sum of money amounts to Rs 780 in two years and Rs 1230 in seven years.Find the principal and rate of interest. 2)In how much time will a sum of money double itself if invested at 8% simple interest per annum?(hint:Let the principal be Rs 100.Interest will also be Rs 100)

Asked by jackalamassery | 27 Jan, 2016, 06:29: PM

Expert Answer

$begin mathsize 14px style 1 right parenthesis space L e t space P r i n c i p a l space b e space P space a n d space R a t e space o f space i n t e r e s t space b e space R. N o w comma space I n t e r e s t space f o r space 2 space y e a r s equals R s. space left parenthesis 780 minus P right parenthesis rightwards double arrow fraction numerator P cross times R cross times 2 over denominator 100 end fraction equals 780 minus P rightwards double arrow P R equals 50 left parenthesis 780 minus P right parenthesis space space space space space space.... left parenthesis 1 right parenthesis I n t e r e s t space f o r space 7 space y e a r s equals R s. space left parenthesis 1230 minus P right parenthesis rightwards double arrow fraction numerator P cross times R cross times 7 over denominator 100 end fraction equals 1230 minus P rightwards double arrow 7 P R equals 100 left parenthesis 1230 minus P right parenthesis space space space space space rightwards double arrow P R equals 100 over 7 left parenthesis 1230 minus P right parenthesis space space space.... left parenthesis 2 right parenthesis F r o m space left parenthesis 1 right parenthesis space a n d space left parenthesis 2 right parenthesis comma 50 left parenthesis 780 minus P right parenthesis equals 100 over 7 left parenthesis 1230 minus P right parenthesis rightwards double arrow fraction numerator 780 minus P over denominator 1230 minus P end fraction equals 2 over 7 rightwards double arrow 5460 minus 7 P equals 2460 minus 2 P rightwards double arrow 5 P equals 3000 rightwards double arrow P equals R s. space 600 S u b s t i t u t i n g space V a l u e space o f space P space i n space left parenthesis 1 right parenthesis comma space w e space g e t 600 R equals 50 left parenthesis 780 minus 600 right parenthesis rightwards double arrow 600 R equals 50 cross times 180 rightwards double arrow R equals fraction numerator 50 cross times 180 over denominator 600 end fraction equals 15 percent sign P l e a s e space p o s t space o n e space q u e r y space a t space a space t i m e. end style$