find unit rate 40 textbooks weigh 120 pounds

Use this proportion, cross multiply and solve for x.

40/120 = 1/x

But how do you know all the textbooks weigh the same amount? Poorly written question..

To find the unit rate, which is the rate of one quantity compared to another quantity, in this case, the weight of the textbooks (in pounds) per textbook, divide the total weight by the number of textbooks.

Unit rate = Total weight / Number of textbooks

Unit rate = 120 pounds / 40 textbooks

Calculating this:

Unit rate = 3 pounds per textbook

Therefore, the unit rate for this scenario is 3 pounds per textbook.