Study the pattern. The figures are made up of black squares.
- How many black squares will there be in Figure 10?
- How many black squares will there be in Figure 35?
- Which figure is made up of 221 black squares?
(a)
Pattern for the number of black squares
Figure
1: 1 x
5 = 1 x (
1 +
4) = 5
Figure
2: 2 x
6 = 2 x (
2 +
4) = 12
Figure
3: 3 x
7 = 3 x (
3 +
4) = 21
Formula
Number of black squares = Figure Number x (Figure Number + 4)
Number of black squares for Figure 10
= 10 x (10 + 4)
= 10 x 14
= 140
(b)
Number of black squares in Figure 35
= 35 x (35 + 4)
= 35 x 39
= 1365
(c)
Figure Number x (Figure Number + 4) = Number of black squares
By guess and check:
Figure Number = 13
13 x 17 = 221 (✔)
13 x (13 + 4) = 221
Figure Number with 221 black squares = 13
Answer(s): (a) 140; (b) 1365; (c) 13
