Question

{4(x+2)=1-5y,3(y+2)=3-2x {2/y+3/x=13,3/y-4/x=3 {x+y=420,30%x

Answer 1

{4(x+2)=1-5y,3(y+2)=3-2x

4x+8=1-5y

4x+5y=-7 (1)

3(y+2)=3-2x

3y+6=3-2x

2x+3y=-3 (2)

(2)*2-(1)

4x+6y-4x-5y=-6+7

y=1

x=-3

{2/y+3/x=13 (1)

3/y-4/x=3 (2)

(1)*4+(2)*3

8/y+12/x+9/y-12/x=13*4+3*3

17/y=61

y=17/61

x=17/33

{x+y=420 (1)

30%x+40%y=160*80%

3x+4y=1280 (2)

(1)*3-(2)

3x+3y-3x-4y=420*3-1280

y=20

x=400