2006 AMC 10A Problems/Problem 3

Problem

The ratio of Mary's age to Alice's age is 3:5. Alice is 30 years old. How many years old is Mary?

$\mathrm{(A) \ } 15\qquad \mathrm{(B) \ } 18\qquad \mathrm{(C) \ } 20\qquad \mathrm{(D) \ } 24\qquad \mathrm{(E) \ } 50$

Solution

We can create the equation

$\frac{3}{5}=\frac{x}{30}$

Where x is Mary's age. Simplfying yields

$(3)(30)=5x\Longrightarrow 90=5x\Longrightarrow x=18, (B)$

See Also

Invalid username
Login to AoPS