A pentagonal prism has two pentagonal faces joined by rectangular faces. How many edges does the prism have?
- 10
- 15
- 7
- 12
Need a hint?
Count the edges of the top and bottom faces, then count the edges that join them.
Worked answer
- Each pentagon has 5 edges, so the two pentagonal faces have 5 + 5 = 10 edges.
- There are 5 vertical edges joining the top and bottom pentagons, one at each corner.
- Total edges = 10 + 5 = 15.
Answer: 15
The mistake this question tests
Habit
Calculation slip
Pupils count only the edges of the two pentagons and forget the 5 vertical edges that join them, getting 10.
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