Question 1107671
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Christina + Paul + Jane = 40


(P-2)     + P    + (P+6) = 40


3P +4 = 40  ====>  3P = 40-4 = 36  ====>  P = {{{36/3}}} = 12.


<U>Answer</U>.  Paul is 12, Christina is 10, Jane is 12+6 = 18 years old.


<U>Check</U>.   12 + 10 + 18 = 40.   ! Correct !
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Forget about systems of equations. There is no any need in it for so simple problem.