Useful Shortcuts and Tricks for Simple Interest & Compound Interest
Simple Interest:
Formula:
1) SI = P x R x T/100
2) Principal = Simple Interest ×100/ R × T
3) Rate of Interest = Simple Interest ×100 / P × T
4) Time = Simple Interest ×100 / P × R
5) If the rate of Simple interest differs from year to year, then
Simple Interest = Principal × (R1+R2+ R3…..)/100
The four variables in the above formula are: SI=Simple Interest P=Principal Amount (This the amount invested)T=Number of yearsR=Rate of interest (per year) in percentage
1). A sum of money is divided into n parts in such a way that the interest on the first part at r1% for t1 years, on the second part at r2% for t2 years, on the third part at r3% for t3years, and so on, are equal. Then the ratio in which the sum is divided in n part is:
1/r1×t1: 1/r2 ×t2: 1/r3×t3
Example:
A sum of Rs 7700 is lent out in two parts in such a way that the interest on one part at 20% for 5 yr is equal to that on another part at 9% for 6 yr. Find the two sums.
Solution:
Here, R1 = 20% R2 = 9%
T1 = 5 yr T2 = 6 yr
By using formula, ratio of two sums = 1/100 : 1/54 = 27 : 50
Therefore, first part = [27/(27+50)]*7700 = Rs 2700
Second part = [50/(27+50)]*7700 = Rs 5000
2). Amount = Principal + S.I = p + [(p x r x t)/100]
