Question

calcule x e y:

a-x/2=y/3 e x+y=40
b-x/y=5/4 e x+y=18

Answer 1

a
x/2 = y/3
multiplica em cruz e separa uma das incógnitas
3x = 2y
x = 2y/3 *** substitui  
x + y = 40
( 2y/3 ) + y/1 = 40/1
mmc = 3
2y + 3y = 120
5y = 120
y = 120/5 = 24 ***

x =  2 ( 24)/3 =  48/3 = 16 ****
b
x/y = 5/4
4x = 5y
x = 5y/4 ***

x + y = 18
5y/4 + y/1 = 18/1
mmc = 4
5y + 4y = 72
9y = 72
y = 72/9 = 8 ****
x = 5 ( 8)/4 = 40/4 = 10 ***