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To Find Principal
When interest, time, rate are given:
Example 5:
What amount was borrowed, for which amount of interest is 200 at the rate of 5% for 4 years.
Solution:
Let P = Principal Rate = 5%
Interest = 200 time = n = 4
I = Interest
We know that
To Find Principal
When amount, rate, time are given:
Example 6:
If the amount for 2 years at 6% is 4,000, what was the principal?
Solution:
Let P = Principal Rate = 6%
n = 2 A = 4,000
We know that
 
To Find Rate
When interest, time, principal are given:
Example 7:
The amount of simple interest for Rs.15,000 for 2 years is 1000, find rate of interest.
Solution:
Let Principal = 15,000
Simple interest = I = 1000
Time = 2 years
Interest = P r n
 
 
Example 8:
At what rate would a sum of money double in 20 years?
Solution:
Let Principal = P
Amount after 20 years = A = 2P
Time = n = 20 years
But, we know
 per annum.
To Find Time
When simple interest, principal and rate are given:
We have
Example 9:
Suppose Rs.700 are invested at 4% per annum. How long will it take for the amount to reach 784?
Solution:
Let P = 700
A = 784
r = 4%
We know that
Example 10:
How long will it take for Rs. 2000 to amount 2360 at 6% per annum simple interest.
Solution:
Let P = 2000
A = 2360
r = 6%
we know that
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