Study the table carefully.
- How many dots are there in Figure 15?
- If there are 21 dots, what Is the Figure number?
(a)
Pattern for the number of dots
Figure 1: (1 - 1) x 5 + 1 = 1
Figure 2: (2 - 1) x 5 + 1 = 6
Figure 3: (3 - 1) x 5 + 1 = 11
Figure 4: (4 - 1) x 5 + 1 = 16
Formula:
Number of dots = (Figure number - 1) x 5 + 1
Number of dots in Figure 15
= (15 - 1) x 5 + 1
= 71
(b)
Figure number for 21 dots
(Figure number - 1) x 5 + 1 = 21
(Figure number - 1) x 5 = 21 - 1 = 20
(Figure number - 1) = 20 ÷ 5 = 4
Figure number = 4 + 1 = 5
Answer(s): (a) 71; (b) 5