Question

Mario’s company makes unusually shaped imitation gemstones. One gemstone has 14 faces and 10 vertices. How many edges does the gemstone have? 

Answer 1

The gemstone has 22 edges.

We use Euler's formula on this:

F + V - E = 2

Substituting our information, we have:

14 + 10 - E = 2

Combining like terms, 
24 - E = 2

Subtract 24 from both sides:
24 - E - 24 = 2 - 24
-E = -22

Divide both sides by -1:
-E/-1 = -22/-1
E = 22