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Thinkful - Number Drills: Blue and red marbles

Description

You and a friend have decided to play a game to drill your statistical intuitions. The game works like this:

You have a bunch of red and blue marbles. To start the game you grab a handful of marbles of each color and put them into the bag, keeping track of how many of each color go in. You take turns reaching into the bag, guessing a color, and then pulling one marble out. You get a point if you guessed correctly. The trick is you only have three seconds to make your guess, so you have to think quickly.

You've decided to write a function, guessBlue() to help automatically calculate whether you should guess "blue" or "red". The function should take four arguments:

  • the number of blue marbles you put in the bag to start
  • the number of red marbles you put in the bag to start
  • the number of blue marbles pulled out so far (always lower than the starting number of blue marbles)
  • the number of red marbles pulled out so far (always lower than the starting number of red marbles)

guessBlue() should return the probability of drawing a blue marble, expressed as a float. For example, guessBlue(5, 5, 2, 3) should return 0.6.

My Solution

def guess_blue(blue_start, red_start, blue_pulled, red_pulled)
  (blue_start - blue_pulled).to_f/((blue_start - blue_pulled) + (red_start - red_pulled))
end