Question

a sum of money is doubled itself in 7 years.find the rate of interest per annum

Answer 1

let the principle be x and r is rate of interest.
Now amount is 2x. so the interest will be 2x-x= x.
Now we know that interest = PRT/100
Here, T is time given = 7 years
so,

$x = x \times r \times 7 \div 100$
$r = 100 \div 7\%$