Activity Studying Prime and Composite Numbers
Discovery lesson: small groups
Objective: students find factors for numbers by arranging
objects in arrays
Materials: disks or other counting materials
䡲 Give each group a paper containing the following
information:
䡲 Make arrays for sets of 2, 3, 5, 7, 11, 13, and 17 disks
and record the results. (Arrays for 7 disks are shown.)
䡲 Determine the array for one disk and record it.
䡲 Ask student to examine the chart for patterns. Students
may answer with statements such as “Some whole numbers—2, 3, 5, 7, 11, 13, 17—have only two arrays.”
䡲 These numbers only make a straight line rather than a
rectangular pattern.
䡲 The number sense has the numeral 1 and the number
䡲 All the possible arrays into which sets of six disks can be
arranged are shown here:
that tells how many disks are in the array:
䡲 “Some whole numbers— 4, 6, 8, 9, 10, 12, 15—have
more than two arrays.”
䡲 These numbers can be arranged in one or more rectangular patterns as well as in straight lines.
䡲 More than two number expressions can be written: 1 ⫻ n
and combinations of other numerals:
䡲 Arrange sets of 4, 8, 9, 10, 12, and 15 disks into all of
䡲 “The number 1 has only one array.”
their possible arrays. Make a record of each array for each
number on the chart.
Whole
Number
6
Arrays
2-by-3, 3-by-2, 6-by-1, 1-by-6
Number of
Different
Arrays
4
Whole
Number
Arrays
Number of
Different
Arrays
1
2
3
4
5
6
7
8
9
10
1-by-1
1-by-2, 2-by-1
1-by-3, 3-by-1
2-by-2, 1-by-4, 4-by-1
1-by-5, 5-by-1
2-by-3, 3-by-2, 6-by-1, 1-by-6
1-by-7, 7-by-1
2-by-4, 4-by-2, 8-by-1, 1-by-8
3-by-3, 9-by-1, 1-by-9
2-by-5, 5-by-2, 10-by-1, 1-by-10
1
2
2
3
2
4
2
4
3
4