Question

Find the rate of interest when rs 800 fetches rs 130 as simple intrest in 2 yrs 6 months

Answer 1

Solution :

Given ,

Principal = Rs. 800

Simple Interest = Rs. 130

Time = 2 * (1/2)

⇒ (2 * 2 + 1/2)

⇒ 5/2

Let the rate of interest be r

Finding the Rate of Interest

r = ( 100 × I )/( pt )

⇒  ( 100 × 130 )/[ 800 × (5/2 ) ]

⇒ ( 100 × 130 )/ ( 400 × 5 )

⇒ 13/2

⇒ 6.5%

Therefore , Our required  rate of interest is 6.5% or 13/2

Answer 2

Principal ( p ) = Rs 800

Simple interest ( I ) = Rs 130

Time ( t ) = 2½ years = (5/2 ) years

Let the rate of interest = r %

We know that ,

I = ( ptr )/100

Or

r = ( 100 × I )/( pt )

*************************************

Now ,

r = ( 100 × 130 )/[ 800 × (5/2 ) ]

=> r = ( 100 × 130 )/ ( 400 × 5 )

After cancellation , we get

= 13/2

= 6.5 %

Therefore ,

Rate of interest = r = 6.5%

Or

r = 13/2 %