Upper Primary Mathematics Fractions - Commonwealth of Learning

3
Example: In a family of 10 children,
5
of the children are boys. How many
3
are boys?
5
3
of 10 is the same as
5
3
× 10. The product of
5
× 10 and 10 ×
3
5
is the same, but the meaning and process is quite different.
Solution
3
To solve of 10 using models, it is convenient to use set models which take
5
the form of an array. In set models, the denominator tells us the number of
elements in each row. The number of rows is determined by the total number
of elements divided by the number of elements in each row (denominator).
3
We will make a rectangular array showing of 10. The number of elements
5
in each row is five and the number of rows is two. In an array of 2 by 5, there
are 3 boys in each row.
Figure 3.2: Rectangular array
There are six boys. How many are girls?
Unit Activity 2
1. Verify that
1
× 8 and 8 ×
1
gives rise to the same answer.
4
4
2. Using models, generate the rule of multiplying a whole number by a
common fraction.
3. Can you find the error made by Jelita. Why would someone compute in
this way?
1 8
× 8 =
4 32
1
4. In a cost saving measure, Judith’s company reduced all salaries by .
8
If Mulenga’s monthly salary was $2400.00, what will he receive now? If
another employee’s salary is $2800.00, what was the old salary?
Module 2: Unit 3 28 Multiplication and Division of Common Fractions