Shortcut 75:
Simple interest
$SI=\frac{PNR}{100}$
P = Principle amount invested or borrowed
R = Rate of interest per term
N = Number of terms
Term = duration for which interest is calculated
Question:
A man invested Rs. 10000 at 4% per annum simple interest. What is the interest he will get at the end of 3 years?
P = 10000; N = 3; R = 4
Substitute the values in the above equation, we get
SI = 10000 x 3 x 4/100
= 1200

Shortcut 76:
Compound interest
$CI=\frac R{100}P+\frac R{100}[Interest till last term]$
Question:
What is the compound interest obtained for Rs. 16000 at 2% per annum for three years?