a class discussion about what it means to double or halve numbers. Ask
students to give some examples of doubling or halving (e.g. half of 4
is 2; double 10 is 20; and so on). Ask students to share some
situations in which they would double or halve numbers (e.g. baking,
making groups, etc.).
Bring a group of students up to the front of the room, such as
5 students, and ask them how they would double the size of the group.
Each student can pick another student to join the group at the front of
Next, bring a group of an even number of students to the front
of the room. Tell them to halve the group. Send half of the group back
to their seats.
Distribute the Baby Weight activity sheet to each student.
Discuss the "rule of thumb" as stated on the activity sheet: A
baby doubles its weight in six months. Complete the first two rows as a
class. Give students time to complete the rest of the chart
Using a red crayon for the birth weights and a brown crayon for
the six-month weights, explain how to complete the bar graph. Students
should pair up and compare their bar graphs. The teacher can circulate
throughout the room to check for accuracy.
You may wish to have students create additional bar graphs for
other babies, similar to the ones in questions 2 and 3 on the activity
sheet using grid paper.
Solutions to the Baby Weight Activity Sheet
The following are the missing numbers from the chart (question 1):
As a class, discuss the similarities and differences between the two
graphs completed (questions 2 and 3 on the activity sheet.) Students
may point out that both graphs are bar graphs and show a comparison
between birth weight and six-month weight. Students may also say that
the graphs show the weights of different babies and the fact that they
"look" different (one is horizontal and one is vertical.
- Parker, Tom. Rules of Thumb. 2 vols. Boston: Houghton Mifflin Co., 1983, 1987.
- Cook, Marcy. "IDEAS: Applications." The Arithmetic Teacher. Vol. 36, No. 8, April 1989, pp. 27-32.