Question

John is 5 years older than Mary. In 10 years, twice John's age decreased by Mary's age is 35, and John's age will be twice Mary's current age. Find their ages now. If x is Mary's age now and y is John's age now, which system of equations could not be used to solve the problem? 1. y = x + 5 and y + 10 = 2x 2. y = x + 5 and 2(y + 10)-(x + 10) = 35 3. y = x + 5 and 2(y + 10) = x

Answer 1

3. y = x+5 and 2(y +10) = x

Explanation:

The variables are defined in the problem statement. The second equation, 2(y+10)=x, says, in effect, ...

... In 10 years, twice John's age will equal Mary's age now.

There is no corresponding statement in the given problem, so this equation is useless for finding the solution.

The solution to the last system of equations is (x, y) = (-30, -25)—not a viable solution to any age problem.