# 4.4. Condition:

In front of the elevator stand people weighing $130,60,61,65,68,70,79,81,83,87,90,91$ and 95 kg. The elevator's load capacity is 175 kg. What is the minimum number of trips needed to get everyone up?
# Answer: 7 (or 13)

## Solution.

In one trip, the elevator can move no more than two people, as the minimum possible weight of three people will be no less than $60+61+65=186>175$. Note that no one will be able to go up with the person weighing 135 kg, so a separate trip will be required for his ascent. Six trips will be needed for the remaining ten people, as no more than 2 people can fit in the elevator. The trips will be as follows: $(60,95),(61,91),(65,90),(68,87),(70,83),(79,81)$ and $(130)$.

In this problem, 13 is also considered a correct answer if the solution takes into account not only the elevator's ascents but also its descents to pick up people.