A thumb-wrestling match requires two thumbs, so we can either suppose that we need at least two people

, or allow one to thumb-wrestle one's self. In either case, we'd have

, so let's just say we need a minimum of two players.
If we add one more person to the set of players, then the first two people would need to play 1 additional match each. So

.
If we add one more person, then the first three people would again each have to play 1 more match with the new person. So

.
And so on, so that in general, the number of games needed for everyone to play exactly one match with everyone else is given recursively by
Answer:
21 students
Step-by-step explanation:
90 x .10 = 9
80 x .15 = 12
9 + 12 = 21 students
Answer:
ok
Step-by-step explanation:
Answer:
X < 7/2
Step-by-step explanation:
Move the variable to the left, separate into possible cases , solve, find the intersections, find the union, and then you get your solution.