Question 678394
LET X, Y & Z BE THE THREE NUMBERS.
X+Y=67 OR X=67-Y
X+Z=80 OR X=80-Z
Y+Z=91
67-Y=80-Z
Y+Z=91 ADD THESE 2 EQUATIONS.
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67+Z=171-Z
Z+Z=171-67
2Z=104 
Z=104/2
Z=52 ANS. FOR Z.
Y+52=91
Y=91-52
Y=39 ANS. FOR Y.
X+39=67
X=67-39
X=28 ANS. FOR X.