Pounds of boxes

Question

A delivery truck is transporting boxes of two sizes: large and small. The combined weight of large box and small box is 80 pounds. The truck is transporting 55 large boxes and 50 small boxes. If the truck is carrying a total of 4300 pounds in boxes, how much does each type of box weigh?

Answer 1

Well, if you have the insight to see that 50 large and 50 small boxes weigh 50(80) = 4000, so the extra 300 lbs is the 5 large boxes.

 

300/5 = 60

 

A small box is 20 lbs.

 

Buuuuut, to do this algebraically...

 

l + s = 80

55l + 50s = 4300

 

Solve the first equation for l or s and substitute into the 2nd equation. Take your result and plug it back into the first equation to solve for the other variable.