thinkful-number-drills-blue-and-red.js

// 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.

// solution

function guessBlue(blueStart, redStart, bluePulled, redPulled) {
  return (
    (blueStart - bluePulled) / (blueStart - bluePulled + (redStart - redPulled))
  );
}