On line segment AE, B is the midpoint of segment AC, C is the midpoint of segment AD, and D is the midpoint of segment BE. DE = 15 mm. How many mm are there in the length of segment AD?

Answer 1

Let AC=CD = x

and

AB = BC = y

Then x = 2y and 15 - y = x

By substitution, 2y = 15 - y

3y = 15

y = 5

then x = 2y = 2(5) = 10

THe entire line segment is 10 + 10 + 15 = 25

AD = 20