7 cows, 21 pigs and 72 hens. The trick to this is finding the combination of cows and hens with the same cost and quantity since pigs are already equal. The magic combination is 7 cows and 72 hens, giving you 79 animals that cost $79 ($70 + $9). Then you just add 21 pigs to get to 100 animals.

At the 3,661st second, the time and date can be written 01:01:01 01/01/01.

That is one cool date :)

The letter E. The series contains all of the letters that rhyme with bee (apologies to any English speakers who pronounce Z as zed instead of zee if this confused you).

Therein

1. the
2. there
3. he
4. in
5. rein
6. her
7. here
8. ere
9. herein
10. therein

With one teller, customers will wait nearly five hours on average. But adding a second teller makes the wait go down to 3 minutes.

Thanks to John D. Cook for this one.