Question

A certain sum lent under simple interest doubles itself in five years. After how many years will the sum become four times itself, if the rate of interest at which it is lent is increased by 5 percentage

Answer 1

Answer

4.29 years

Explanation

Formula to calculate simple interest :

A = P(1 + rt)

A certain sum lent under simple interest doubles itself in five years.

Suppose, certain sum = P

2P = P (1 + r5)

2P/P = (1 + r5)

2 = (1 + r5)

2-1 = r5

1 = r5

1/5 = r

The sum become four times itself, if the rate of interest at which it is lent is increased by 5 percentage

4P = P ( 1 +(0.5+r) t)

put value of r

4P/P = ( 1+(0.5 +1/5) t )

4 = ( 1 + 0.7t )

4 - 1 = 0.7t

3 = 0.7t

3/0.7= t

t=4.29 years

Answer 2

Explanation:

Answer

4.29 years

Explanation

Formula to calculate simple interest :

A = P(1 + rt)

A certain sum lent under simple interest doubles itself in five years.

Suppose, certain sum = P

2P = P (1 + r5)

2P/P = (1 + r5)

2 = (1 + r5)

2-1 = r5

1 = r5

1/5 = r

The sum become four times itself, if the rate of interest at which it is lent is increased by 5 percentage

4P = P ( 1 +(0.5+r) t)

put value of r

4P/P = ( 1+(0.5 +1/5) t )

4 = ( 1 + 0.7t )

4 - 1 = 0.7t

3 = 0.7t

3/0.7= t

t=4.29 years