Quantitative Aptitude ( Numbers )

Numbers ; IMPORTANT FACTS AND FORMULAE

1. Natural Numbers :

Counting numbers 1, 2, 3, 4, 5, .. are called natural numbers.

II. Whole Numbers :

All counting numbers together with zero form the set of whole numbers. Thus,

I. 0 is the only whole number which is not a natural number.

II. Every natural number is a whole number.

III.Some Important Formulae :

I. ( 1 + 2 + 3 + .....+ n) = n (n + 1 ) / 2

II. (1 2 + 22 + 32 + ..... + n2) = n ( n + 1 ) (2n + 1) / 6

III. (1 3 + 23 + 33 + ..... + n3) = n2 (n + 1)2 / 4