How Old Is John Now?

[mathdad]

John’s father is 5 times older than John and John is twice as old as his sister Alice. In two years time, the sum of their ages will be 58. How old is John now?

John's dad = 5(2x)

John = 2x

Alice = x

5(2x) + 2 + 2x + 2 + x + 2 = 58

10x + 3x + 6 = 58

13x + 6 = 58

Correct so far?

 

[Greg]

Yes. Why didn't you solve for x and use that value to compute John's age? :)

Will you try rewriting the system so John's age is the variable?

 

[mathdad]

John's dad = 5(2x)

John = 2x

Alice = x

5(2x) + 2 + 2x + 2 + x + 2 = 58

10x + 3x + 6 = 58

13x + 6 = 58

13x = 58 - 6

13x = 52

x = 52/13

x = 4

John = 2x

John = 2(4)

John is 8 years old.