Answer
a) At least two of them come from the same subset. Two such integers
have a sum of 9, as desired
b) No
Work Step by Step
a)
Group the first eight positive integers into four subsets of two integers each so that the integers of each subset add up to 9: {1, 8},
{2, 7}, {3, 6}, and {4, 5}.
--If five integers are selected from the first eight positive integers,
--by the pigeonhole principle:
-ced.
b)
-No. Take {1, 2, 3, 4},
