Mathematics 21 Online
OpenStudy (anonymous):

can anyone help me on this problem? "Mary's age is twice Fred's age and 1/3 of Sally's age. If the sum of their ages is 99 how old are they?

Let's call Mary's age $$m$$, Fred's age $$f$$, and Sally's age $$s$$. Then: \begin{align} m &= 2f\\ m &= \frac{s}{3}\\ m + s + f &= 99 \end{align} We can solve this system of equations first by solving for $$s$$ in terms of $$m$$: $s = 3m$ We already have $$m$$ in terms of $$f$$, which means we have $$s$$ in terms of $$f$$ as well: $$s = 3m = 3(2f) = 6f$$. So we can plug into the last equation to solve for $$f$$: \begin{align} 2f + 6f + f &= 99\\ 9f &= 99\\ f &= 11 \end{align} Is this enough for you to find the other ages?

OpenStudy (anonymous):

oh my goodness yes i think that helps SO much! THANK YOU!!!

Great!

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