Answer:
David is 12 years old.
Step-by-step explanation:
Let r = Rebecca's age
Let d = David's age
let p = Dad's age
David is 3 times as younger than his dad:
d = [tex]\frac{p}{3}[/tex]
David is 2 times older than Rebecca:
d = 2r
Rebecca is 30 years younger than the dad:
r = p-30
All three equations can be solved by a system
2r = [tex]\frac{p}{3}[/tex]
r = p-30
multiplying r = p-30 by negative 2 and adding it to 2r = [tex]\frac{p}{3}[/tex]
0 = (-2p + p/3) + 60
multiplying new equation by 3
0 = (-6p + p) + 180
5p = 180
p = 36
d = 36/3 = 12
