Subtraction Instruction

The above two equations have the same value and are very straightforward. It is important to know that the order of numbers is significant in subtraction (and division). Different ordering will result in different answers. For example:

Some complications arise when larger numbers are used and you need to carry numbers.

Example

(A)
The first task is to subtract the right most column. Because 9 is larger than 3, a unit has to be borrowed from the column to the left. The 4 in the middle column is reduced to 3, and the one is added to the right column, making the first row 13 - 9 = 4.

(B)
The second task is to subtract the second column. The same process is repeated. Borrow a 1 from the left column to allow the subtraction. The top number in the left column becomes 6, while the top number in the centre column becomes 13. 13 - 8 = 5. The left column would then be subtracted. 6 - 5 = 1.

Note: If subtracting more than 2 numbers, you cannot stack the numbers as you would in addition. Instead, work from the first subtraction to the last, two numbers at a time.

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Subtraction Practice Tests

Work through the following tests to make sure you are comfortable with the material.

Practice Questions

Try these practice questions. The answers are posted below.

a) 82 - 15 =

b) 192 - 77 =

c) 112 - 76 =

d) 521 - 125 =

e) 221 - 91 =

f) 724 - 215 =

g) 91 - 47 =

h) 125 - 83 =

i) 6512 - 1050 =

j) 1010 - 101 =

Answers

a) 67
b) 115
c) 36
d) 396
e) 130
f) 509
g) 44
h) 42
i) 5462
j) 909