Question

What is the sum of $x,y$ and $z$ ?
$x+y=8$
$x+z=11$
$y+z=7$

• A. $12$
• B. $13$
• C. $21$
• D. $11$

Answer 1

Answer: (B)

13: It is possible to solve for $x,y$ and $z$ individually, but you will save a significant amount of time by solving for the combo. What is $x+y+z$?

The equations collectively contain exactly two "copies" of each variable and these variables are always added. Add the three equations together:

$x+y=8$

$x+z=11$

$x+y+z=7$

-------------------------

$2x+2y+2z=26$

Divide the equation by $2:x+y+z=13$