Double Trouble

Like the activities on pages 16–17, this activity is designed to make students familiar with arrays and to use them to help develop their multiplication strategies. The strategies on this page focus on doubling and using fives, so the students need some prior knowledge of these processes.
Model two lots of 7 on a bead frame or use an overhead projector with an overhead transparency of a bead frame and coloured transparencies of different bead combinations. The students may know that 7 + 7 = 14. Ask them to look at how they could use the groups of fives to work it out another way. There are two fives and four more. The differentiated colours on the bead frame make this very clear for the students. You could record this as: two lots of 7 is 7 + 7 = 14 and
(2 x 5) + (2 x 2) = 14.
As an extension, you could ask the students what other times tables they could work out from knowing that 8 x 6 = 48. Discuss how to adjust the answer 48 to give the answers to 7 x 6 and 9 x 6. Model eight lots of 6 on the bead frame and add or remove one more group of 6.

Answers to Activity

1. a. 14. (2 x 5) + (2 x 2)
b. 28. 14 x 2 (double the answer for 2 lots of 7) or (4 x 5) + (4 x 2)
c. 56. 28 x 2 (double the answer for 4 lots of 7) or (8 x 5) + (8 x 2)
2. a. 2 x 10 = 20
4 x 10 = 40 or 2 x 20 = 40
8 x 10 = 80 or 2 x 40 = 80
b. 2 x 9 = 18
4 x 9 = 36 or 2 x 18 = 36
8 x 9 = 72 or 2 x 36 = 72
c. 2 x 8 = 16
4 x 8 = 32 or 2 x 16 = 32
8 x 8 = 64 or 2 x 32 = 64