The following is a sequence of structures made by joining identical cubes with 1-cm sticks as edges.
- How many sticks are needed to make structure 17?
- How many sticks are needed to make structure 140?
- A structure is made using 108 sticks. Which structure is it?
(a)
Pattern for the number of sticks
Structure 1: 1 x 8 + 4= 12
Structure 2: 2 x 8 + 4 = 20
Structure 3: 3 x 8 + 4 = 28
Formula
Number of sticks = Structure number x 8 + 4
Number of sticks for structure 17
= 17 x 8 + 4
= 140
(b)
Number of sticks for structure 140
= 140 x 8 + 4
= 1124
(c)
Number of sticks = Structure number x 8 + 4
Structure number = (Number of sticks - 4) ÷ 8
Structure number for structure made with 108 sticks
= (108 - 4) ÷ 8
= 104 ÷ 8
= 13
Answer(s): (a) 140; (b) 1124; (c) 13