16 Answers to Exercises
1 Let’s Count!
1.1 A Party
1.1.1. 7 · 6 ··· 2 ·1 = 5040.
1.1.2. Carl: 15· 23 = 120. Diane: 15· 3 · 2 ·1 = 90.
1.1.3.Bob: 9· 7 · 5 ·3 = 945. Carl: 945· 25 = 302,40. Diane: 945· 5 · 4 · 3 · 2 ·1=
113 ,400.
1.2 Sets and the Like
1.2.1. (a) all houses in a street; (b) an Olympic team; (c) class of ’99; (d)
all trees in a forest; (e) the set of rational numbers; (f) a circle in the plane.
1.2.2. (a) soldiers; (b) people; (c) books; (d) animals.
1.2.3. (a) all cards in a deck; (b) all spades in a deck; (c) a deck of Swiss
cards; (d) nonnegative integers with at most two digits; (e) nonnegative
integers with exactly two digits; (f) inhabitants of Budapest, Hungary.
1.2.4. Alice, and the set whose only element is the number 1.
1.2.5. No.
1.2.6. ∅,{ 0 },{ 1 },{ 3 },{ 0 , 1 },{ 0 , 3 },{ 1 , 3 },{ 0 , 1 , 3 }. 8 subsets.
1.2.7. women; people at the party; students of Yale.