Addison is 3 times as old as Bailey, and Bailey is 2.5 times as old as Christopher. If the sum of their ages is 66, how old is Christopher?

6 years old

Step-by-step explanation:

First, turn the information given in words as equations. Use variables to represent the people:

let A be Addison's age

let B be Bailey's age

let C be Christopher's age

A = 3B (Addison is 3 times as old as Bailey)

B = 2.5C (Bailey is 2.5 times as old as Christopher)

A + B + C = 66 (the sum of their ages is 66) (sum means addition)

Start with the equation for the sum of their ages (A + B + C = 66). You have other equations that can replace the variables in this equation.

A + B + C = 66

(3B) + B + C = 66 Replace A with 3B (because A = 3B)

4B + C = 66 Collect like terms (3B + B = 4B)

4 (2.5C) + C = 66 Replace B with 2.5C (because B = 2.5C)

10C + C = 66 Collect like terms (10C + C = 11C)

11C = 66 Isolate "C"

11C/11 = 66/11 Divide both sides by 11 to cancel out 11 on the left side.

C = 6 Christopher's Age

Therefore Christopher is 6 years old.