Question

3x + y = 19 , and x + 3y = 1. Find the value of 2x + 2y
a. 20
b. 18
c. 11
d. 10
e. 5

Answer 1

$3x+y=19 \\ x+3y=1 \\ \\ \hbox{add the sides of the equations:} \\ 3x+x+y+3y=19+1 \\ 4x+4y=20 \\ \\ \hbox{divide both sides by 2:} \\ 2x+2y=10$

The answer is d. 10.