To solve any questions relating to ages, I find it easier to make a table, like in the picture below.
See picture for answer and clear diagram.
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Notes/Explanations + answer in written form
Jennies age now = x
So Georges age now would be: x + 12 (since he is 12 years older)
Jennies age in 5 years would be: x + 5 (since it is 5 years later)
Georges age in 5 years would be: x + 12 + 5 = x + 17
We are told that their ages in 5 years would add up to 50. So we can write an equation like so:
x + 17 + x + 5 = 50 (All you have to do now is solve it)
2x + 22 = 50 (combine like terms)
2x = 28 (subtract 22 from both sides)
x = 14 (divide both sides by two)
That means that Jennies age is 14 years
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Note:
Please comment below if you have any questions - I would be more that happy to help / explain anything!