Multiple ways to add and subtract

I am learning to use multiplication and division to solve addition and subtraction problems.

Below is an array. You can see it has 4 rows and 6 faces in each row. We can refer to this as 4 X 6 = 24

Here is an array showing 2 X 6 = 12

Let’s add the two arrays together.4 X 6 = 24 plus 2 X 6 = 12. 24 + 12 = 36

Watch what happens when we combine the two arrays.

Now we have 6 X 6 = 36 Let’s look a little more closely.

(4 X 6) + (2 X 6) = 6 x 6 We can combine the 4 and the 2 together because they both have the common multiple of 6.

Now let’s use this strategy for an actual question. Craig has 28 marbles, Sarah has 9 marbles and Joe has 45 marbles. How many marbles do they have in total?

27 + 9 + 45 = ? Step 1: Think of a number which is a factor of all these numbers. 9

(3 X 9) + (1 X 9) + (5 X 9) Step 2: We can combine these to make the question below.

9 X 9 = 81

We can also use this strategy for subtraction. Alicia has read 56 books this year. 24 of these were fiction books. How many of these were not fiction.

56 – 24 = ?Step 1: Think of a number which is a factor of both 56 and 24.

Step 2: (7 groups of 8) – (3 groups of 8) = (4 groups of 8)

8

(7 X 8) - (3 X 8) = ?

4 X 8 = 32

Now try these questions on your own. Remember to first find a common factor.

Need some more practise? Try Pg68 of Teacher Tools Addition and Subtraction Book Numeracy resources

1) 66 + 42 + 12 = ?

2) 25 + 35 + 50 = ?

3) 16 + 28 + 12 = ?

4) 81 - 63 = ?

(11 X 6) + (7 X 6) + (2 X 6) = 20 X 6

(5 X 5) + (7 X 5) + (10 X 5) = 22 X 5

(4 X 4) + (7 X 4) + (3 X 4) = 14 X 4

(9 X 9) - (7 X 9) = 2 X 9

120

110

56

18