Question 1192644
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Shelia's age plus Kerry's age is 27
Shelia's age plus jack age is 38
Kerry's age plus jack age is 33
How old is jack?
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From the condition, you have these three equations 

    S + K = 27    (1)

    S + J = 38    (2)

    K + J = 33    (3)

-------------------------  Add equations (1), (2) and (3).   You will get


    2S + 2K + 2J = 27 + 38 + 33

    2S + 2K + 2J =      98


Divide both sides by 2

    S + K + J = 49    (4)


To find Jack age, subtract equation (1) from equation (4).  You will get then

            J = 49 - 27

            J =   22.


<U>ANSWER</U>.  Jack is 22 years old.
</pre>

Solved.


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This problem is of very special class of problems.

They admit very special method of solution, which I showed you in this post.


It is worth to be memorized.