SOLUTION: Hello, I am just struggling how to set up the problem. I know how to solve it, it's just forming the equation is what troubles me. Bob is 15 years older than his sister. In ten

Question 943086: Hello, I am just struggling how to set up the problem. I know how to solve it, it's just forming the equation is what troubles me.
Bob is 15 years older than his sister. In ten years, Bob will be twice as old as his sister will be. How old are they now?
It's a substitution method question. Is the first part x=y + 15? I can't figure out the second half. Please help!!

Answer by richard1234(7193) (Show Source): You can put this solution on YOUR website!
First, define your variables clearly. What are x and y? To minimize confusion, let b and s be Bob's and her sister's ages now.

b = s+15 (Bob is 15 years older than his sister)
b+10 = 2(s+10) (Bob, in 10 years, is twice as hold as his sister, in 10 years)

Replace b with s+15 in the second equation and solve for s.
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