Roughly how many?
Purpose
In this activity we look at cubes which have been roughly sorted into arrays and decide about how many there are. We use our knowledge of multiplication facts to estimate the number of cubes.
Achievement Objectives
NA3-2: Know basic multiplication and division facts.
Specific Learning Outcomes
use arrays to solve estimation problems
Required Resource Materials
Multilink cubes
Overhead projector (if available)
Activity
- Tell the students that you are going to show them some cubes and that they have to figure out about how many there are. Tell the students that you will be asking them more than or less than questions.
- Put 16 cubes on the projector, arranged roughly in 4 rows of 4. Display for a couple of seconds.
Did you see more than 20 cubes? Why do you think that? - Repeat the activity with a slightly different number of cubes. Say 17 cubes in 4 rows of 4 and a row of 5. More than 5 cubes per row and more than 5 rows is hard to visualise quickly.
Did you see more than 20 cubes? Why do you think that?
- Continue with different numbers of cubes.