Hello, I’m Anushka studying in class VI, I have summarize few formulae to brush-up at the time of exams specially in my Olympiad exam. This will help a lot at eleventh hour of exam.

**Formula # 1. how to calculate no of diagonals?**

Ans: n(n-3)/2

where n is the no of sides, e.g. in rectangle , n=4, so 4(4-3)/2 = 2 ( no of diagonals)

**Formula #2. How to sum of consecutive no starting from 1?**

Ans: n(n+1)/2

e.g. sum of first 5 , it means, 1 + 2+3+4+5 = 5(5+1)/2 = 15