Multiplication and Division
Primary 3 · Mathematics
Multiplication and Division
Lesson 1 of 3
12 min
Mugisha is helping at his aunt's stall in Kimironko market. On the table there are 6 bunches of bananas, and every bunch has exactly 5 bananas.
He starts adding out loud. "Five, and five more is ten, and five more is fifteen..." His aunt laughs kindly. "There is a faster way," she says.
That faster way is called multiplication. Today it becomes yours.
Picture 4 plates. Each plate has 3 mandazi on it. No plate has more, no plate has fewer. We call these equal groups.
To find the total you can add: 3 + 3 + 3 + 3 = 12. There are 12 mandazi.
Adding the same number again and again is called repeated addition. It gives the right answer, but it is slow, and it is easy to lose your place.
Instead of writing 3 + 3 + 3 + 3, we write 4 × 3.
The sign × means groups of. So 4 × 3 is read "four groups of three", or simply "four times three".
4 × 3 = 12. The same answer, with much less writing.
number of groups × size of each group = total
Let us go back to the market and do it slowly, step by step.
Step 1. Count the groups. There are 6 bunches, so there are 6 groups.
Step 2. Look inside one group. Each bunch holds 5 bananas.
Step 3. Write the number sentence. Six groups of five: 6 × 5.
Step 4. Work it out by counting in fives, one bunch at a time: 5, 10, 15, 20, 25, 30. That is six jumps, and you land on 30.
6 × 5 = 30. Mugisha's aunt has 30 bananas on the table, and Mugisha found out in four quick steps.
In your classroom the desks stand in straight lines. There are 3 rows, and each row has 5 desks.
A neat picture like this, in straight rows and columns, is called an array.
Count by rows: 3 rows of 5 desks. 5 + 5 + 5 = 15, so 3 × 5 = 15.
Now turn your head and look down the columns instead. There are 5 columns, and each column has 3 desks. 3 + 3 + 3 + 3 + 3 = 15, so 5 × 3 = 15.
Nobody moved a single desk, so of course the total is still 15.
You just saw something useful: 3 × 5 = 15 and 5 × 3 = 15.
You can swap the two numbers around and the answer stays exactly the same.
This saves you work. If 8 × 2 feels hard, swap it. 2 × 8 is just double 8, which is 16. So 8 × 2 = 16 as well.
7 × 1 means seven groups with 1 thing in each group. That is simply 7 things. So 7 × 1 = 7.
7 × 0 means seven groups with nothing in them. Seven empty baskets hold nothing at all. So 7 × 0 = 0.
Tip
Say the × sign as "groups of". Then 4 × 3 tells you its own story: four groups of three. Draw four circles, put three dots in each, and count them.
And keep the swap trick close. If a times sum looks scary, turn it around. 9 × 2 is much friendlier as 2 × 9 — that is just double 9, which is 18.
Work each one out on paper first. Then tap Show answer to check.
What you learned today
Quick check
Which is the same as 5 + 5 + 5?
