Question

GEOMETRY. PLEASE CHECK MY ANSWER! THANKS.
Mario’s company makes unusually shaped imitation gemstones. One gemstone had 12 faces and 10 vertices. How many edges did the gemstone have?

A. 23 edges
B. 22 edges
C. 25 edges
D. 20 edges****

Answer 1

I'd solved it in the pic, and the answer is D. 20

Answer 2

This is simple.
we should have a knowledge of the Euler's Theorem/Euler's Formula
F+V=E+2
Basically states that:
# of Faces+ # of Vertices= # of Edges+2
12 + 10 = E + 2
(-2) + 22 = E + 2 (-2)
           20 = E

Yep, The answer is D. 20 edges