Question

X+y/5-x-y/4=7/20
x+y/3-x-y/2+5/6=0
???

Answer 1

$\frac{x + y}{5} - \frac{x - y}{4} = \frac{7}{20} \\ 4x + 4y - 5x - 5y = 7 \\ 4 \: {x + y} - 5 \: {x + y} = 7 \\ {4 - 5} \: \: \: \: {x + y} = 7 \\ - 1 \: \: \: \: x + y = 7 \\ - x - y = 7 \\ x + y = - 7$

$\frac{x + y}{3} - \frac{x - y}{2} + \frac{5}{6} = 0 \\ \frac{ - 7}{3} + \frac{7}{2} + \frac{5}{6} = 0 \\ \frac{ - 14}{6} + \frac{21}{6} + \frac{5}{6} = 0 \\ \frac{12}{6} = 0 \\ 2 \: \: unequal \: to \: 0$