Week 18 · Unknown factors and equal parts · 3 lessons
2
Sharing a cookie fairly
Discover Mathematics P3: Term 2, Lessons 61–70
GoalShare a whole fairly into equal parts and name halves, thirds and fourths.
New words
equal parts · parts that are exactly the same sizehalf · 1 of 2 equal partsthird · 1 of 3 equal partsfourth · 1 of 4 equal parts, also called a quarter
Explanation
A fair share means that every part is the same size. When we cut a whole into equal parts, we give the parts names. A whole cut into 2 equal parts has halves. A whole cut into 3 equal parts has thirds. A whole cut into 4 equal parts has fourths, also called quarters. One part is one half, one third or one fourth. All the parts together make the whole again: 2 halves, 3 thirds or 4 fourths make 1 whole. If the parts are not the same size, they are not halves, thirds or fourths. To make halves of a paper, fold it so that the two edges match exactly and the crease divides it into two equal parts.
Worked examples
Two children share one big cookie. They cut it into 2 equal parts. Each child gets one half. The two halves make 1 whole cookie.
Three friends share a cookie. They cut it into 3 equal parts. Each friend gets one third. Three thirds make 1 whole.
Fold a square of paper in half, then fold it in half again. Open it. There are 4 equal parts, so each one is a fourth. Four fourths make 1 whole.
Class activity
Fair shares. Take a piece of paper or a flatbread. Fold or cut it into halves, then do the same with another piece for thirds and one more for fourths. Check each time that the parts are exactly the same size by laying one on top of another.
Practice
1
A pizza is cut into 3 equal pieces. What is each piece called?
Each piece is one third.
2
Mariam cuts a flatbread into 2 pieces, but one piece is much bigger than the other. Are these halves?
No. Halves must be equal in size, so these are not halves.
3
The strip is cut into equal parts and one part is shaded. What is the shaded part called?
There are 3 equal parts and 1 is shaded, so it is one third.
4
Karim folds a paper so that the two edges match exactly. How many equal parts are there, and what are they called?
