30% x + 40% y =79 30% (x+y) = 66 obliczcie mi to plis

30% x + 40% y =79 30% (x+y) = 66 0.3x + 0.4y = 79/ *10 0.3(x+y)= 66/*10 3x + 4y= 790 3x+3y=660/ *(-1) 3x+4y= 790 -3x-3y=-660 3x+ (-3x) + 4y+(-3y)= 790+(-660) y= 130 3x= 660 - 390 y= 130 x=90

nie jestem pewna: 30%x+40%y=49/*100 30%(x+y)=66/*100 30x+40y=4900 30(x+y)=6600 3x+4y=490 3x+3y660 4y=490-3x/:4 3x+3y=660 y=122.5-3x 3x+3(122.5-3x)=660 y=122.5-3x 3x+367.5-9x=660 y=122.5-3x -6x+367.5=660 y=122.5-3x -6x=292.5/:(-6) y=122.5+3x x=48.75 y=122.5-146.25 x=48.75 y=-23.75