Question

A zum of money placed at ci doubles itself in 4 years .It will amount to eight times in ?

Answer 1

Let,Principal=Rs.100

Amount=Rs.200

Rate=r%

Time=4years

Now,

A=P×[1+(r100)]n200=100×[1+(r100)]42=[1+(r100)]4−−−−−−(i)

If sum become 8 times in the time in years then,

8=(1+(r100))n23=(1+(r100))n−−−−−−(ii)

Usingeqn(i)in(ii),

weget([1+(r100)]4)3=(1+(r100))n[1+(r100)]12=(1+(r100))n

Thus,n=12years.