SOLUTION: how old is jack and kylie's grandfather? the digits of his age add to 15, his age is an even number, he is younger than 90

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Question 1185430: how old is jack and kylie's grandfather? the digits of his age add to 15, his age is an even number, he is younger than 90
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39617)   (Show Source): You can put this solution on YOUR website!
Which is which? Who is what?

Throw out the question, first sentence. Only the second sentence description appears to have some meaning.

t, tens digit
u, units digit
and further, .

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Answer by ikleyn(52781)   (Show Source): You can put this solution on YOUR website!
.

There is only one two-digit even positive integer number less than 90 with the sum of digits 15.

This number is 78. 

    The proof is OBVIOUS.

    The last digit must be even, and there is only one working possibility for it, which is "8".

    Hence, the tens digit is  15-8 = 7.

So the grandfather's age is 78 years.

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Probably, the question's accurate form should be

        how old is jack's and kylie's grandfather?       (meaning one grandfather to two grandchild)
        the digits of his age add to 15, his age is an even number, he is younger than 90.




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