Question

Claire is twice as old as david. together their ages total 9 years. how old is each of then

Answer 1

So,

Let c represent Claire's age and d represent David's age.

c = 2d
c + d = 9

Substitute 2d for c in the second equation.
2d + d = 9

Collect Like Terms.
3d = 9

Divide both sides by 3.
d = 3

Substitute 3 for d in the first equation.
c = 2(3)
c = 6

Claire is 6 years old and David is 3 years old.

Answer 2

We have a system here, letting C = Claire's age and D = David's age,


`\left \{ {{C=2D} \atop {C+D=9}} \right.`

Substituting C=2D into the 2nd equation,

C+D = 9

2D+D = 9

D = 3

Substituting D=3 back into the first equation,

C=2D

C=2*3

C=6

Therefore Claire is 6 and David is 3.

Hope that helped!

~Cam943