Stretching the metaphor, but your jellybeans were in a group to start with, so halving it makes sense. Changing the sign is harder, but let's say your group of

Stretching the metaphor, but your jellybeans were in a group to start with, so halving it makes sense. Changing the sign is harder, but let's say your group of jellybeans was actually a loan, and you borrowed from two people... beans / -2