Your father gives you $100 to go to town and buy 100 chickens, the prices are as follows:
You have to buy at least one of each kind of chicken, what are the numbers of each kind of chicken you need?
Solution:
Well, I kinda cheated to get the answer. I wrote a Qbasic program to figure all the permutations that work. I did optimizes it, I went though the Chicks in steps of 2 (to get rid of the decimal). I also only went up to 20 Hens because at that point you are already out of money. But other then that I just did the equivalent of smashing the circle block in to the square slot with a hammer.
Here are my answers, I got a total of 11:

1 Rooster
91 Hens
8 Chicks

2 Roosters
82 Hens
16 Chicks

3 Roosters
73 Hens
24 Chicks

4 Roosters
64 Hens
32 Chicks

5 Roosters
55 Hens
40 Chicks

6 Roosters
46 Hens
48 Chicks

7 Roosters
37 Hens
56 Chicks

8 Roosters
28 Hens
64 Chicks

9 Roosters
19 Hens
72 Chicks

10 Roosters
10 Hens
80 Chicks

11 Roosters
1 Hen
88 Chicks