there is a difference between a person trying to solve a 7kyu, i guess, it is not at all a 7 kyu at least needs to be 5 kyu. of course for "dan's" it might be a single line, but the complexity level should be set according to a person most likely to solve it i.e. a newbee.

Thanks, I have fixed it.

As stated: However, if 0 heads and 0 legs are given always return [0, 0] since zero heads must give zero animals. so returning (0, 0) (as a single type) would not be viable. This is because a return value of "No solutions" is not mathematically possible, however (0, 0) is possible - provided there aren't any cows or chickens in the first place.

I do agree that "No solutions" (as a string) is a bit stupid and a null value should be returned instead, however it is a bit late since 1751 people have passed. So I don't see the need in changing it because it doesn't change the functionality of the Kata.

Thanks for the suggestion though!

6 lines. ;)

Generating primes is actually so (much) a common task on CW that, after a few weeks/months, you will look back at this one and gently laugh at your own comment. ;) (but well... 6 kyu wouldn't have hurt, I guess, yes. ;) )

Agree... I think 6 kyu is fair enough... =)