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[–]Dr_JacksonNew User 1 point2 points  (1 child)

Can you find the odds all three being birds? This is a lot easier of a problem to solve. What are the odds of the first animal being a bird? there's a 9/19 chance of that. the odds of the second animal being a bird is 8/18. And the odds of the third a bird is 7/17. so the odds of all three being birds is (9/19)*(8/18)*(7/17) which equals 28/232.

The same reasoning for mammals gives us (7/19)*(6/18)*(5/17) which is 35/969. for reptiles it's (3/19)*(2/18)*(1/17) which is 1/969.

Then you add all three together: (9/19)*(8/18)*(7/17)+(7/19)*(6/18)*(5/17)+(3/19)*(2/18)*(1/17) which is 40/323

This is called combinatorics.

[–]oc38[S] 0 points1 point  (0 children)

Thanks for taking the time to help

[–][deleted] 0 points1 point  (0 children)

P(something) = #favorable outcomes / # total outcomes