Answer:
20
Explanation:
Given that the triangles are similar, we know that the corresponding side lengths should all have similar ratios.
This means that ab/ef = bc/fg = ca/ge as they're corresponding.
We know that ge = 8, ca = 4, ab = 10 and we want to find ef
Remember ab/ef = ca/ge so 10/ef = 4/8
4/8 = 10/ef
==> cross multiply
80 = 4ef
==> divide both sides by 4
20 = ef
We can test our answer by seeing if the ratios are the same
ab/ef = 4/8 = 1/2
ca/ge = 10/20 = 1/2
The ratios are the same, therefore our answer is correct.