The simple interest on a sum of money for 10 years is Rs 3130. If the principal becomes 5 times after 5 years, then what will be the total interest (in Rs)obtained after 10 years?

first method:
interest after 10 years = 3130

so after 5 years = 1565

so, now principal = 1565*5 = 7825

thus total interest for 10 years = 7825+1565 = 9390

second method:

si= prt/100

p*r*10 / 100 = 3130  so  p*r = 31300

now,

si = si for 1st five years + si for 2nd five years

si = p*r*5/100 + 5p*r*5/100 

put value of pr in the above equation

si = 31300* 5/100 + 5*31300*5/100

si= 9390

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