The age of Mary, Jo, and Larry have a sum of 120. Mary's age is three times Jo's age, and Larry's age is 5 less than Jo's age. Find the age's of Mary, Jo, and Larry. And fill in these blanks. If Mary's age is 75 then Jo's is ... and Larry's age is ...

Assume Jo's age is x.

Mary is 3x, Larry is x-5

So x + 3x + (x-5) = 120

x = 25

So Jo is 25, Mary is 25*3 = 75, Larry is 25-5 = 20

Let M = Mary's age.

Let J = Jo's age

Let L = Larry's age.

The sum of their ages is 120. Therefore

M + J + L = 120 (1)

Mary's age is three times Jo's age. Therefore

M = 3J (2)

Larry's age is 5 less than Jo's age. Therefore

L = J - 5 (3)

Substitute (2) and (3) into (1).

3J + J + (J-5) = 120

3J + J + J - 5 = 120

5J - 5 = 120

5J = 120 + 5 = 125

J = 125/5 = 25

Therefore

J = 25, M = 3J = 75, L = J - 5 = 20

Answer: Mary's age = 75; Jo's age = 25; Larry's age = 20

If Mary's age is 75, then Jo's age is 25, and Larry's age is 20.