A delivery person uses a service elevator to bring boxes of books up to an office. The delivery person weighs 140 lb and each box of books weighs 40 lb. The maximum capacity of the elevator is 1130 lb. How many boxes of books can the delivery person bring up at one​ time?

We know that since the delivery person must be in the elevator with the boxes of books, there will definitely be a 140 pound object in the elevator.
As such, we can reduce the maximum capacity accounting for the delivery person’s weight.

So this new maximum capacity would be 1130 - 140= 990 pounds

Now we can use the new maximum capacity to find the number of boxes the elevator can hold. We know the boxes are 40 pounds each and the maximum capacity is 990 pounds. From this, we can find how many boxes by dividing through, which tells us how many 40 pound boxes will fit.

990/40=24.75 boxes

However, since we can’t take books out of the box or cut the box into smaller parts, the number of boxes must be 24. This is because 25 would be too much and it can only be an integer value.

Thus, the delivery person can bring up 24 boxes of books at one time