Who saw
Written on 11:25 pm by Vja Students
Abel, Mabel, and Caleb 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 Abel saw, two were yellow. Of the birds Mabel saw, three were yellow. Of the birds Caleb saw, four were yellow. How many yellow birds were seen in all? How many non-yellow birds were seen in all?
Ans: Three birds were seen by one person each, three were seen by each unique pair (Abel-Mabel, Abel-Caleb, and Mabel-Caleb), and one was seen by all three. So seven birds were seen in all, and each person saw a total of four. Hence, all of the birds Caleb saw were yellow. These four birds are: (1) the one Caleb saw alone, (2) the one Caleb saw with Abel, (3) the one Caleb saw with Mabel, and (4) the one all three saw together. This accounts for both of the yellow birds Abel saw, and two of the three yellow birds Mabel saw. The third yellow bird Mabel saw could not have been the one Abel and Mabel saw together, because Abel only saw two yellow birds; so the third yellow bird Mabel saw must have been the one she saw alone.
So five yellow birds were seen (the one Mabel saw, the one Caleb saw, the one Abel and Caleb saw, the one Mabel and Caleb saw, and the one all three saw), and two non-yellow birds were seen (the one Abel saw and the one Abel and Mabel saw) by the group.
Is it 5 ?
Apart from the 4 Caleb saw ( 1 alone, 1 with Mabel, 1 with Abel, 1 that all saw together ), there is one yellow bird that only Mabel saw.
There were total 7 birds seen by all-
5 Yellow
2 Non Yellow
If you have only one match and you walked into a room where there was an oil burner, a kerosene lamp, and a wood burning stove, which one would you light first?
1. The fire
2. The match, of course
3. The lantern
4. The stove