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International Baccalaureate · PYP 1

Multiplication: Equal Groups

⌚ ~82 min ▢ 8 blocks ✓ 36 exercises ➣ Prerequisites : Ordinal Numbers and Patterns, Addition Within 20
I Groups and Skip Counting

How many cubes are there?
Figure

There are 3 groups of 5 cubes. We can count by 5s: 5, 10, 15. There are 15 cubes.


Proposition — Counting by 5s
To count by 5s, we start at \(0\) and add \(5\) each time. The shaded numbers are the numbers we reach: \(0\), \(5\), \(10\), \(15\), …
Figure
Method — Counting Equal Groups
When objects are arranged in equal groups, we do not need to count them one by one. We count by the size of one group, once for each group. We say: \(4\) times \(5\) — the word times tells how many equal groups there are.
Here there are \(4\) groups of \(5\) cubes. We count by 5s, and we say one number for each group:
Figure
We reach \(5\), \(10\), \(15\), \(20\): there are \(20\) cubes in all.
Example
A box holds \(10\) pencils. How many pencils are there in \(3\) boxes?
Figure

There are \(3\) groups of \(10\) pencils. We count by 10s, one number for each box: \(10\), \(20\), \(30\).
Figure
There are \(30\) pencils.

Skills to practice
  • Skip Counting by 5s
  • Choosing the Right Count
  • Counting Groups of 2
  • Counting Groups of 5
  • Counting Groups of 10
  • Counting Groups with the Word “Times”
II Solving Group Problems
Method — From a Story to a Repeated Addition
  1. Find the groups: Read the story and find how many groups there are.
  2. Find the size: Find how many objects are in each group.
  3. Write the repeated addition: Write the size of one group once for each group, with \(+\) signs between them.
  4. Skip-count: Skip-count by the size of one group (by 2s, by 5s or by 10s) to find the total.
Example
For the birthday party, Léa prepares 4 plates with 5 cherries on each plate. How many cherries does she use?
Figure

  • There are \(4\) groups (the plates), with \(5\) cherries in each group.
  • We write one number for each plate: \(5+5+5+5\).
  • We count by 5s, one number for each plate:
    Figure
  • \(5+5+5+5=\textcolor{colorprop}{20}\). Léa uses \(\textcolor{colorprop}{20}\) cherries.

Skills to practice
  • From a Story to a Repeated Addition
III Going further
Skills to practice
  • Writing Repeated Additions with Pictures
  • Quiz