The figure shows a series of steps built using square cubes. The n number of steps is given by x -step.
- How many square cubes were used if n is 9?
- How many square cubes were used if n is 55?
- Find the number of steps if a total of 169 cubes are used.
Figure number |
Number of square cubes |
Area (cm2) |
Perimeter (cm) |
1 |
1 |
4 |
8 |
2 |
3 |
12 |
16 |
3 |
6 |
24 |
24 |
4 |
10 |
40 |
32 |
9 |
(a) |
... |
... |
(a)
Pattern for the number of square cubes
1-step: 1 = 1
2 = 1
2-step: 1 + 3 = 2
2 = 4
3-step: 1 + 3 + 5 = 3
2 = 9
Number of square cubes = Step number
2 Number of square cubes for 9-step
= Sum of odd numbers
= Step number
2 = 9
2 = 81
(b)
Number of square cubes for 55-step
= Sum of odd numbers
= Step number
2 = 55
2 = 3025
(c)
Number of square cubes = Step number
2 Number of steps = √Number of square cubes
Number of steps for 169 square cubes
= √169
= 13
Answer(s): (a) 81; (b) 3025; (c) 13