Question

a sum of money at simple interest doubles in 10 years in how many years the same rate it will be tripled

Answer 1

Let P=100, A=200,It means I=100

Now We want A=300,means I=200

Years for I of Rs. 100 =10

Years for I of Rs. 200=(10/100)*200

=20 Years

Answer 2

Define x:

Let the principal amount be x

Find the total interest for the 10 years:

The sum at simple interest rate doubles in 10 years

⇒ The amount at the end of 10 years is 2x

⇒ Interest = 2x - x = x

Find the interest rate for 1 year

Interest in 10 years = x

Interest in 1 year = x ÷ 10 = 0.1x

Find the amount when it is tripled:

Total amount = 3x

Total interest earned = 3x - x = 2x

Find the number of years needed:

Number of years needed = 2x ÷ 0.1x =  20 years

Answer: 20 years