A, B and C went bird watching. Each of them saw one bird that none of the others did. Each pair saw one bird that the third did not. And one bird was seen by all three. Of the birds A saw, two were yellow. Of the birds B saw, three were yellow. Of the birds C saw, four were yellow.

(a) How many yellow birds were seen in all?
(b) How many non-yellow birds were seen in all?

Each person spotted 4 birds. All the birds C spotted were yellow. That means that the bird all of them spotted was yellow (1 yellow, 0 non-yellow). That also means that the bird C and A both spotted is yellow and the bird C and B both spotted is yellow (3 yellow, 0 non-yellow). The bird only C spotted also must have been yellow. A spotted 2 yellow birds and 2 non-yellow birds. The 2 yellow birds A spotted were: the bird all three of them spotted and the bird that C and A both spotted. That means that the bird A and B spotted and the bird that only A spotted were non-yellow (4 yellow, 2 non-yellow). 1 of the 3 yellow birds that was spotted was the bird all three of them saw. Another one was the bird that both B and C spotted. The non-yellow bird B spotted was the one that both B and A spotted. That leaves the bird that just B spotted to be yellow (5 yellow, 2 non-yellow).

Edited on August 30, 2003, 12:41 pm

Posted by Kelsey on 2003-08-30 12:26:51