Answer:
4851 ways
Step-by-step explanation:
The fish have 3 choices. They can make it above, below, or though the pipe. Keep in mind there are 100 fish total:
group 1 + group 2 + group 3 = 100
If we keep group 3 (the fish that swim below the pipe) constant, say 1, and increment the other two (group 2 starting off at 1) we find 98 possibilities.
98 + 1 + 1 = 100,
97 + 2 + 1 = 100,
96 + 3 + 1 = 100
. . . 98 possibilities
Now we take group 1 as one greater (1 + 1 = 2) and then start incrementing group 2 starting from 1 as done before. So 97 + 2 + 1 = 100. Followed by 96 + 3 + 1, 95 + 4 + 1...97 possibilities
If we continue this pattern, we have 98 + 97 + 96... + 1 total possibilities to partition this school of fish.
98 + 97 + 96... + 1,
Sum = n(n + 1)/2 = 98(98 + 1)/2 = 98(99)/2 = 4851
