Question

at what rate a sum doubles itself in 8 year 4 months

Answer 1

Let principal(P)=100
Time(T)=8year4 month ALWAYS Convert into years
=8+1/3=25/3 years
NOW USING RATE =(SI*100)/PT
=100*100/(100*(25/3))
=100*3/(25)
=4*3
=12%

HOPE THIS HELPS YOU .

Answer 2

Answer:  Rate of interest = 12%

Step-by-step explanation:

Let the Principle be 'P'.

Let the Amount be '2P'

Let the rate of interest be 'R'

Number of years = 8 yrs 4 months

As we know the formula for "Simple Interest ":

$Interest= Amount-Principal=2P-P=P\\\\Interest=\frac{P\times R\times T}{100}\\\\P=\frac{P\times R\times 8\frac{4}{12}}{100}\\\\1=\frac{25\times R}{300}\\\\R=\frac{300}{25}=12\%$

Hence, Rate of interest = 12%