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A solid has faces that consist of 5 congruent squares and 4 congruent equilateral triangles. The solid has 9 vertices. How many edges does the solid have? (no image)

A.

16 edges

B.

18 edges

C.

20 edges

D.

22 edges

Verified Answer :

JcAlmighty

The answer is A. 16 edges

For most of the solid shapes, we can use Euler's polyhedron formula:
f + v - e = 2
f - the number of faces
v - the number of vertices
e - the number of edges

We know:
f = 5 + 4 = 9
v = 9
e = ?

So:
f + v - e = 2
9 + 9 - e = 2
18 - e = 2
18 = e + 2
e = 18 - 2
e = 16

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