Quantitative Aptitude Notes: Simplification

Mentor for Bank Exams

Quantitative Aptitude Notes on Simplification

BASIC FORMULAE
1. (a+b) 2=a2+b2+2ab 
2. (a−b) 2=a2+b2−2ab
3. (a +b) 2− (a−b) 2=4ab   
4. (a+b) 2+ (a−b) 2=2(a2+b2)
5. (a2–b2)= (a+b) (a−b)  
6. (a+b+c) 2=a2+b2+c2+2(ab+bc+ca)
7. (a3+b3) = (a+b) (a2−ab+b2)    
8. (a3–b3) = (a−b) (a2+ab+b2)
9. (a3+b3+c3−3abc)= (a+b+c) (a2+b2+c2−ab−bc−ca)
10. If a+b+c=0, then a3+b3+c3=3abc.
TYPES OF NUMBERS

1. Natural Numbers:
Counting numbers 1, 2, 3, 4, 5 … are called natural numbers

2. 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.

3. Integers:
All  natural  numbers,  0  and  negatives  of  counting  numbers i.e.,…,−3,−2,−1,0,1,2,3,….. together form the set of integers.
(i) Positive Integers: 1, 2, 3, 4….. is the set of all positive integers.
(ii) Negative Integers: −1, −2, −3… is the set of all negative integers.
(iii) Non-Positive and Non-Negative Integers: 0 is neither positive nor negative. 
So,  0,1,2,3,….  represents  the  set  of  non-negative  integers,  while 0,−1,−2,−3,….. represents the set of non-positive integers.

4. Even Numbers:
A number divisible by 2 is called an even number, ex. 2, 4, 6, 8, etc.

5. Odd Numbers:
A number not divisible by 2 is called an odd number. e.g. 1, 3, 5, 7, 9, 11 etc.

6. Prime Numbers:
A number greater than 1 is called a prime number, if it has exactly two factors, namely 1 and the number itself.

7. Composite Numbers:
Numbers  greater  than  1  which  are  not  prime,  are  known  as composite numbers, e.g., 4,6,8,9,10,12.
Note: 
(i) 1 is neither prime nor composite.
(ii) 2 is the only even number which is prime.
(iii) There are 25 prime numbers between 1 and 100.

REMAINDER AND QUOTIENT:

"The remainder is r when p is divided by k" means p=kq+r the integer q is called the quotient.

EVEN ,ODD NUMBERS

A number n is even if the remainder is zero when n is divided by 2: n=2z+ 0 or n=2z.
A number n is odd if the remainder is one when n is divided by 2: n=2z+1.
even X even = even
odd X odd = odd
even X odd = even
even + even = even
odd + odd = even
even + odd = odd
Some important tricks
    1. 1 + 2 + 3 + 4 + 5 + … + n = n(n + 1)/2
    2. (12 + 22 + 32 + ..... + n2) = n ( n + 1 ) (2n + 1) / 6
    3. (13 + 23 + 33 + ..... + n3) = (n(n + 1)/ 2)2
    4. Sum of first n odd numbers = n2
    5. Sum of first n even numbers = n (n + 1)