Weight of empty box

Question

A box containing 15 copies of the same novel weighs 4 pounds. The same box containing 11 copies of the same novel weighs 3 lbs. 2 oz. How many ounces does the empty box weigh?

Answer 1

b +15n= 4 lbs

b +11n = 3 lbs 2 ounces

subtract to get

4n = 4 lbs - 3lbs - 2 oz

n = 1 lb. - 3/4 lbs - 1/2 oz

copy of the novel weighs 1/4 lb - 1/2 oz = 3.5 oz

the box weighs 4 - 15(1/4 lb - 1/2 oz)

= 1/4 lb + 7.5 oz

= 11.5 ounces

check the answer

16 oz = 1 lb

11.5 + 15(3.5) = 11.5+ 52.5 = 64 oz = 4 lb

11.5+11(3.5) = 11.5 + 38.5 = 50 oz = 3 lbs 2 oz