Joe Doe (joe_doe_zero) wrote in 0_arithmetic,
Joe Doe
joe_doe_zero
0_arithmetic

General subtraction - lesson 1

Subtracting two or more numbers is almost as easy as adding two or more numbers. There are a few things that need to be cleared, however.

Let's say we want to do: 9 - 5 - 3

This can mean two things: Either (9 - 5) - 3 or 9 - (5 - 3). The answers to them are different. Remember that we must do what is written in the parenthesis first.

In the first statement:

(9 - 5) - 3

9 - 5 = 4
4 - 3 = 1

(9 - 5) - 3 = 1

In the second statement:

9 - (5 - 3)

5 - 3 = 2
9 - 2 = 7

9 - (5 - 3) = 7

Very different answers. Remember that subtraction is not commutative so the rule, generally, is to do what is in the parenthesis first. Do the inner parentheses first and work your way outward.

((9 - 2) - 3) - (2 - 1)
(7 - 3) - (2 - 1)
4 - 1
3

((9 - 2) - 3) - (2 - 1) = 3

Subtracting numbers with more than one digit


Let's say we want to do 95 - 33.

95 - 33 = ?

We do it in the same way as addition but using subtraction instead of addition.

9 - 3 = 6
5 - 3 = 2

95 - 33 = 62

78 - 54

7 - 5 = 2
8 - 4 = 4

78 - 54 = 24

And now let's move on to the more fun lesson in subtraction - borrowing tens.
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