PSLE Sam uses toothpicks to form figures that follow a pattern. The first four figures are shown.
- The table shows the number of toothpicks used for each figure. Complete the table for Figure 9 and Figure 10. Give your answers in numbers. (Eg 1, 2)
- What is the difference in the number of toothpicks that Sam would use for Figure 13 and Figure 15?
- How many toothpicks would he use for Figure 20?
(a)
Number of toothpicks used:
Figure 1: 15 = 11 + 4 x 1Figure 2: 18 = 10 + 4 x 2Figure 3: 23 = 11 + 4 x 3Figure 4: 26 = 10 + 4 x 4The formula for the total number of toothpicks used is different for odd-numbered patterns and even-numbered patterns.
Number of toothpicks for odd-numbered figure = 11 + 4 x Figure number
Number of toothpicks for even-numbered figure = 10 + 4 x Figure numberNumber of toothpicks used for Figure 9
= 11 + 4 x 9
= 11 + 36
= 47
Number of toothpicks used for Figure 10
= 10 + 4 x 10
= 10 + 40
= 50
(b)
Since every 2 jumps has the same increase,
difference in the number of toothpicks for Figure 13 and 15 = 8
(c)
Figure 20 is an even number.
Number of toothpicks that Sam would use for Figure 20
= 10 + 4 x Figure number
= 10 + 4 x 20
= 10 + 80
= 90
Answer(s): (a) 47, 50; (b) 8; (c) 90
