Question 1027198
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If (Mr. X + Mrs. Y = 69 years) and (Mr. X + Mr. Z = 72 years) and (Mrs. Y + Mr. Z = 79 years).

So, how old are Mr. X, Mrs. Y and Mr. Z?
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<pre>
X + Y     = 69,      (1)
X     + Z = 72,      (2)
    Y + Z = 79.      (3)

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

2X + 2Y + 2Z = 69 + 72 + 79 = 220,  

or

X + Y + Z = 110.     (4)

Now distract (1) from (4). You will get 
Z = 110 - 69 = 41.

Now distract (2) from (4). You will get 
Y = 110 - 72 = 38.

Now distract (3) from (4). You will get 
X = 110 - 79 = 31.

<U>Answer</U>. X = 31, Y = 38, Z = 41.
</pre>

For similar problems, see the lesson <A HREF=https://www.algebra.com/algebra/homework/Matrices-and-determiminant/The-trick-to-solve-some-word-problems-with-three-and-more-unknowns.lesson>The tricks to solve some word problems with three and more unknowns using mental math</A> in this site.