Chapter 7: Raksha Bandhan

On Raksha Bandhan, sisters tie colourful rakhis on their brothers' wrists. If there are 4 sisters and each has 3 brothers, how many rakhis will be tied? This chapter is all about quickly finding such answers using multiplication.

What we'll learn

See multiplication as repeated addition.
Build the multiplication tables of 2, 3, 4, 5 and 10.
Read arrays , rows and columns of things.
Use the times sign correctly.
Solve simple word problems with multiplication.

The big idea

If 5 plates each have 4 puris, the total is 4 + 4 + 4 + 4 + 4. That is 20 puris. Writing the same addition five times is tiring. Multiplication is a shortcut: 5 × 4 = 20. We say "five fours are twenty".

A multiplication has three parts. In 5 × 4 = 20, the "5" tells how many groups, the "4" tells how many in each group, and "20" is the total. We can switch the order , 4 × 5 also equals 20. That is the magic of multiplication.

Arrays make this very clear. Picture 3 rows of mangoes with 6 mangoes in each row. Counting by rows: 6 + 6 + 6 = 18. Counting by columns: 3 + 3 + 3 + 3 + 3 + 3 = 18. Both ways, we get 18. So 3 × 6 = 6 × 3 = 18.

Tables are friends to memorise slowly. The table of 10 is the easiest , just add a zero. The table of 5 has a fun pattern: 5, 10, 15, 20... ending in 5 or 0. The table of 2 is just doubling.

Let's explore

Rakhi count. Draw 4 hands. On each hand draw 3 rakhis. Count the total. Write it as a multiplication.

Array of biscuits. Lay out biscuits in 3 rows of 5. Count rows and columns. Write the multiplication two ways.

Skip counting. Jump on the floor while saying the table of 4: "4, 8, 12, 16, 20..." up to 40.

Family meal. If your family has 5 people and each eats 2 chapatis, how many chapatis does Amma make? Now if each eats 3?

Worked examples

Example 1. Each rakhi packet has 6 rakhis. There are 5 packets. How many rakhis in all?

5 groups of 6 = 5 × 6.
6 + 6 + 6 + 6 + 6 = 30.
5 × 6 = 30 rakhis.

Example 2. A row has 7 chairs. There are 3 rows. How many chairs?

3 × 7 = 21.
There are 21 chairs.

Example 3. Find 8 × 5 using the table of 5.

5, 10, 15, 20, 25, 30, 35, 40.
The 8th number is 40.
So 8 × 5 = 40.

Quick check

Write 4 + 4 + 4 + 4 + 4 as a multiplication.
What is 6 × 3?
Complete the table of 4: 4, 8, 12, ?, ?, 24.
There are 9 trees and each has 2 mangoes. Total mangoes?
Is 3 × 5 the same as 5 × 3?

Recap

Multiplication is a quick way to do repeated addition.
Swapping the numbers does not change the answer.
Tables help us multiply without counting again and again.