Question

Mr. Cal Q. Later has a bag of jellybeans. As he walks around the room, he places a few jellybeans on everyone's desk—everyone's, that is, except Leo. On Leo's desk he places the bag with the remaining jellybeans. Here are the numbers:
17: Harumi
14: Melissa
13: Marcus and Evelyn
12: Kim, Toby and Lori
11: Jason
9: Efram and Inga
8: Hannah
6: Geoff
3: Luc
2: Muriel
Muriel and Luc are not worried because they know that Mr. Later is fair. Mr. Later tells the students that Leo's jellybeans are all that remain in the bag. If they figure out how many are in there, they will each get to eat the average number of jellybeans which is 10. How many jellybeans are in Leo's bag?

Answer 1

If we add up the number of jelly beans of the 10 listed students, we have 95 jelly beans.

The average number being 10 for each student, and there are 10+Leo=11 students, so the total number of jelly beans is 11*10=110.

Number of jelly beans Leo received must be 110-95=15 jelly beans.