Upper Primary Mathematics Fractions - Commonwealth of Learning

5 1 4 1 3 2
1 1
a) 2 – 1 = 1 b) 4 – 2 = 2 c) 9 – 3
2
= 6
6 6 6 4 4 4
2
Peter simply looks for a greater fraction then subtracts the lesser one from it.
He does not care whether the greater fraction belongs to the minuend or to
the subtrahend. Peter thinks subtraction of common fractions is commutative.
Remedial
1
Interpret 4
4
3
– 2
4
as take-away. Use models to illustrate the problem. In
3
your process of modelling, ask Peter if he can subtract
4
1
from . Also ask
4
1
him for other names for 4
4
1
such as 4 +
4
5
and 3 + .
4
Unit Activity 4
Shanzuwa has difficulty when adding common fractions. Can you find his
pattern of error? Why might Shanzuwa be using such a procedure? How can
you help him?
2 1 4
3 1
a) + = b) + =
3 4 7
4 4
Practice Activity 4
In your classroom, identify errors made by pupils. At times ask them how
they arrived at their wrong answers. Then identify causes of the error and
remember to provide effective remedial work.
Self Assessment
1. Formulate and write a word problem involving real life situations for
1 5
1
2
+ . Use set models to arrive at the answer.
6
2. Find common fractions to fill in the circles so that each diagonal adds up
to the same number. Describe the procedure you used.
Continues on next page
Module 2: Unit 2 22 Addition and Subtraction of Common Fractions
4
8