Very nice, but use double quotes for string interpolation only!

Same bro xD.This was my first attempt seems I am getting a hang of it :)

Ruby fixed.

not according to the Ruby style guide

Turns out i hit my head hard after i submitted - because i missed about the i flag :D

Isn't better to use oneliner like:
def square a; a*a end

Not a legitimate solution but may expose the message error in Ruby:

def solution(a, b)
  false
end

Not sure how to reproduce this. Please provide some example code.

Does it handle strings and symbols for keys?

True, also won't work if somebody gave the hash a non-falsey default value

Of course that depends on the number of "special operations" you need to perform. Since it's fine for the current test cases, why bother with writing it out as a while loop?

If there would be a test case which does give this problem, rewriting it to a non-recursive form is the first thing one would do...

Indeed. Who needs floating point math? ;)

agreed, still failing w/ test error