Question

a sum of money becomes 8 / 5 of itself in 5 years at a certain rate of simple interest find the rate of interest

Answer 1

HI ,  Let Principal = Rs P

 Time ( T ) = 5 years

 Amount ( A ) = Rs 8p/5

 Let rate of interest = R

  Simple interest ( I ) = A - P

  I = 8p/5 - P

 I = ( 8P - 5P )/5

 l = 3P/5 ---( 1 )

 We know that ,

 I = ( PTR )/100 ---( 2 )  From ( 1 ) and ( 2 )

 3P/5 = ( P × 5 × R )/100

 ( 3P × 100 )/( P × 5 × 5 ) = R  

After cancellation ,

 12 = R

 Therefore ,
 Rate of interest = R = 12%

 I hope this helps you.

 : )  

Answer 2

Let the principal be P

Amount = 8 /5

given T = 5 yrs

SI = A - P

A = 8 /5p

A = 8p / 5-p

SI = 3p -5

Again SI = prt / 100

3p /5 = prt / 100

3 / 5 = 5r / 100

R = 3*20 /5

R = 3 *4

R = 12

so interest is 12%