Christian is 3 times as old as Marie. Marie is 12 years younger than Christian. How old is Christian?
C = 3M
C - M = 12
Substitute 3M for C in the second equation and solve for M. Insert that value into the first equation to solve for C. Check by putting both values into the second equation.
Thank you, PsyDAG. I needed this for a 5th grader.
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To find out how old Christian is, let's represent their ages using variables. Let's say Christian's age is C, and Marie's age is M.
According to the information given:
1) Christian is 3 times as old as Marie: C = 3M
2) Marie is 12 years younger than Christian: M = C - 12
Now we have two equations with two variables. We can rearrange the equations to solve for C.
From equation 2, we can substitute C - 12 for M in equation 1:
C = 3(C - 12)
To solve this equation, distribute the 3:
C = 3C - 36
Combine like terms by subtracting 3C from both sides:
C - 3C = -36
-2C = -36
Divide both sides by -2:
C = -36 / -2
C = 18
Therefore, Christian is 18 years old.