Answer:
Marc's age is 12
Step-by-step explanation:
Let
x ----> Marc's age
y ---> Tony's age
z ---> Ben's age
we know that
the sum of their ages is 40
so
[tex]x+y+z=40[/tex] -----> equation A
Marc is half as old as Tony
so
[tex]x=\frac{y}{2}[/tex]
[tex]y=2x[/tex] ----> equation B
Marc is three times as old as Ben
so
[tex]x=3z[/tex]
[tex]z=\frac{x}{3}[/tex] ----> equation C
substitute equation B and equation C in equation A
[tex]x+2x+\frac{x}{3}=40[/tex]
solve for x
[tex]\frac{10x}{3}=40[/tex]
[tex]x=40(3)/10\\x=12\ years[/tex]
therefore
Marc's age is 12
