☰ Year plan · Mathematics

Multiplication and swapping factors

Week 5 · Multiplication equations and swapping factors · 3 lessons
3

Array block game and story problems

Discover Mathematics P3: Term 1, Lessons 11–20
GoalUse arrays of blocks and drawings to solve multiplication story problems.
New words
story problem · a maths problem told with a storysolve · find the answermodel · objects or a drawing that show the problem
Explanation

A story problem tells about equal groups. Read it and ask two questions: how many groups are there, and how many are in each group? Then follow four steps. First, build or draw an array. Second, write the multiplication equation. Third, find the product by repeated addition. Fourth, write the answer with its unit. For 6 rows of 4 chairs, the equation is 6 × 4 = 24 because 4 + 4 + 4 + 4 + 4 + 4 = 24. There are 24 chairs. Check by swapping the factors: 4 × 6 = 24.

Worked examples
Omar buys 4 packs of stickers with 7 stickers in each pack. The equation is 4 × 7 = 28. Skip counting: 7, 14, 21, 28. Omar has 28 stickers.
A microbus has 9 rows of seats with 4 seats in each row. The equation is 9 × 4 = 36. Skip count by 4: 4, 8, 12, 16, 20, 24, 28, 32, 36. There are 36 seats.
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Marina puts 3 flowers in each of 8 vases. The tape shows 8 equal parts of 3. 8 × 3 = 24, so she uses 24 flowers.
Class activity

Array block game. You need 30 small blocks, beans or buttons, and a die. Roll the die twice. The first number is the number of rows and the second is the number in each row. Build the array, write the equation and the product. After 5 rolls, the player with the biggest total wins.

Practice
1
There are 5 rows of 6 chairs in a hall. How many chairs are there?
2
Ahmed has 7 boxes with 3 pencils in each box. How many pencils does he have?
3
A page of stickers has 4 rows with 9 stickers in each row. How many stickers are on the page?
4
Write a story problem for 6 × 5 = 30.
5
Rahma says 8 boxes with 5 books in each make 8 + 5 = 13 books. What is her mistake? What is the right answer?