Each figure is made up of a number of identical straws of 1-cm length.
- Find the perimeter of Figure 23.
- Find the number of straws in Figure 87.
- Given that a figure has a perimeter, P, of 494 cm, find the number of squares in this figure.
Figure Number |
Number of squares |
Number of triangles |
Perimeter (P) |
Number of straws |
1 |
1 |
2 |
6 |
8 |
2 |
2 |
4 |
10 |
15 |
3 |
3 |
6 |
14 |
22 |
4 |
4 |
8 |
18 |
... |
... |
... |
... |
... |
... |
8 |
... |
... |
... |
... |
(a)
Pattern for perimeter in cm
Figure 1: 1 x 4 + 2 = 6
Figure 2: 2 x 4 + 2 = 10
Figure 3: 3 x 4 + 2 = 14
Perimeter = Figure number x 4 + 2
Perimeter for Figure 23
= 23 x 4 + 2
= 94 cm
(b)
Pattern for the number of straws
Figure 1: 1 x 7 + 1 = 8
Figure 2: 2 x 7 + 1 = 15
Figure 3: 3 x 7 + 1 = 22
Number of straws = Figure number x 7 + 1
Number of straws in Figure 87
= 87 x 7 + 1
= 610
(c)
Perimeter = Figure number x 4 + 2
Figure number = (Perimeter - 2) ÷ 4
Figure number with the perimeter 494 cm
= (494 - 2) ÷ 4
= 492 ÷ 4
= 123
Pattern for the number of squares
Figure 1: 1
Figure 2: 2
Figure 3: 3
Number of squares = Figure number
Number of squares for Figure 123 = 123
Answer(s): (a) 94 cm; (b) 610; (c) 123