SOLUTION: John is 4 years older than his sister Mary. Together, their ages add up to 30. How old is Mary

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Question 1108522: John is 4 years older than his sister Mary. Together, their ages add up to 30. How old is Mary

Answer by ikleyn(52777) About Me  (Show Source):
You can put this solution on YOUR website!
.
J - M =  4,
J + M = 30.
------------------To solve the system, add the two equations.

Answer. J = 17, M = 13.