# SOLUTION: a shipment of computer monitors, some weighing 25lb and the others weighing 40 lb each, has a total weight of 680 lb. If there are 20 monitors altogether, how many weigh 40 lb?

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 Click here to see ALL problems on Systems-of-equations Question 390706: a shipment of computer monitors, some weighing 25lb and the others weighing 40 lb each, has a total weight of 680 lb. If there are 20 monitors altogether, how many weigh 40 lb?Answer by checkley79(3039)   (Show Source): You can put this solution on YOUR website!25x+40y=680 x+y=20 x=20-y 25(20-y)+40y=680 500-25y+40y=680 15y=680-500 15y=180 y=180/15 y=12 40 lb. monitors. x+12=20 x=20-12 x=8 25 lb. monitors. Proof: 25*8+40*12=680 200+480=680 680=680