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To Find Principal
We are given n, A, and r
We have to find P by the formula
 
Example 14:
Find principal, when compound interest for 4 years at 6% is 525.
Solution:
Let Principal = P
r = 6%
C.I = 525
We know that
Example 15:
Find principal of Rs.4635.50 due at the end of 3 years at 5% annually.
Solution:
Let Principal = P
A = 4635.50
r = 5%
Using 
 
 
To Find Time
When P, A, r are given
We have to find time by the same formula.
Example 16:
In how many years a sum of 600 would amount to 757.48 at 6% compounded annually.
Solution:
Let Principal = 600
A = 757.48
r = 6%
Using 
Taking log both sides
To Find Rate
When P, n, A are given
We have to find r by the using same formula
Example 17:
Find the rate of interest compounded per annum for 3 years so that 4000 becomes 4635.50
Solution:
Let A = 4635.50
P = 4000
r = ?
Using 
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