Joanna is 15 years younger than Anna. Now after 10 years Anna will be twice the age of Joanna. Find their present age?
J = A - 15
J+10 = (1/2)(A+10)
A - 15 + 10 = A/2 + 5
A/2 = 10
A = 20
J = 5
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check
2(5+10) = 20+10
30 = 30 sure enough