1. The sum of the internal angles of a polygon of n sides is ” (n - 2)* 180″ degrees.
2. Total no of diagonals of a polygon of n sides is ‘nC2 - n’ = n(n-3)/2.
3. Product of r consecutive integers is always divisible by r!.
4. Any no (other than 1) can be expressed in the form of 3k-1,3K or 3k+1.
5. Area of a triangle = 1/2*a*b*sin(x) (a,b are the sides and x the included angle).
6. Any no in the no system is of the form 7K,7k-1,7K+1,7k-2,7K+2,7k-3,7K+3.
7. After 5^4 the remainder left when 5^n is divided by 1000 is 125 when n is odd and 625 when n is even.
8. Relative speed of the hands of a clock = 55 spaces/hr = 5.5 degree/min.
9. In a pie chart 1% = 3.6 degree, 1 degree = 2.78%.