Page 124 - New Medley 5 Semester 2

Calculation of Principal, Rate of Interest and Time

To compute the simple interest, we use the following formula
P × R × T
S.I. =
100

We can also find any one out of the four terms used in the above formula
when three are given, in the following ways:

S.I. × 100 S.I.×100 S.I.×100
P = , R = and T =
R×T P× T P×R

Example 3: In how many years, on `800 at the rate of 6% per

annum, the interest will be `240?

Solution: Given, P = `800, R = 6% and S.I. = `240
S.I. ×100
We know, T =
P× R

240×100
\ T = = 5 years
800× 6

Example 4: At what percent of interest rate, a sum of `1200 will
be `1584 in 4 years?

Solution: Given, P = `1200, A = `1584 and T = 4 years

As S.I. = A – P

So, S.I. = `1584 – `1200 = `384

S.I. ×100
Now, R =
P× T

384× 100
\ R = = 8%
1200 ×4
1
Example 5: For what sum of money at 7 % interest rate, the
2

interest would be `360 in 5 years?

1 15
Solution: Given, R = 7 % = %, S.I. = `360 and T = 5 years
2 2

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