# Aptitude – Shortcuts for Addition and Subtraction

Addition is one of the four basic operations of arithmetic, with the others being subtraction, multiplication and division.

The addition of two whole numbers is the total amount of those quantities combined.

Addition of numbers close to multiples of ten (e.g. 19, 29, 89, 99 etc.)
116 + 39
= 116 + (40 – 1)
= 116 + 40 – 1  —> add 40 then subtract 1
= 156 – 1
= 155

Examples:

There are 1030 books in the library. We bought 67 more books for the library. How many books are there in the library now?

.’.1030 + 67 = 1097

There are 1097 books in the library now.

Problems:

1.116 + 97
= 116 + (100 – 3)
= 116 + 100 – 3   —> add 100 then subtract 3
= 216 – 3
= 213
12.5 + 6.25
= (12 + 0.5) + (6 + 0.25)
= 12 + 6 + 0.5 + 0.25   —> add the integers then the decimals
= 18 + 0.5 + 0.25
= 18.75
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Subtraction is a mathematical operation that represents the operation of removing objects from a collection.

It is signified by the minus sign (−).

SHORTCUTS IN SUBTRACTION:

Subtraction by numbers close to 100, 200, 300, 400, etc.
250 – 96
= 250 – (100 – 4)
= 250 – 100 + 4    —> subtract 100 then add 4
= 150 + 4
= 154

216 – 61
= 216 – (100 – 39)
= 216 – 100 + 39
= 116 + (40 – 1)  —> now the operation is addition, which is much easier
= 156 – 1
= 155

Subtraction of decimals
47 – 9.9
= 47 – (9 + 0.9) —> “double subtraction”
= 47 – 9 – 0.9   —> subtract the integer first then the decimal
= 38 – 0.9
= 37.1

Examples:

Jessica has 1135 beads. 604 beads are red and the rest are blue. How many blue beads does she have?

.’.   1135 – 604 = 531

Problems:

1.250 – 196
= 250 – (200 – 4)
= 250 – 200 + 4    —> subtract 200 then add 4
= 50 + 4
= 54

2.18.3 – 0.8
= 18 + 0.3 – 0.8
= (18 – 0.8) + 0.3  —> subtract 0.8 from 18 first
= 17.2 + 0.3
= 17.5

/aptitude-shortcuts-multiplication/