Me a bag contains only red and blue marbles. yasmine takes one marble at random from the bag. the probability that she takes a red marble is 1 in 5. yasmine returns the marble to the bag and adds five more red marbles to the bag. the probability that she takes one red marble at random is now 1 in 3. how many red marbles were originally in the bag?

a 10 red b 2 red c 5 red d 3 red

C. 5 Red marbles

Step-by-step explanation:

If she started with 5 red marbles and had a probability of 1/5 of drawing a red marble, then there were 20 blue marbles, and 25 total marbles.

   5/25 = 1/5

If she added 5 red marbles, she now would have 10 red marbles and still 20 blue marbles, giving her 30 total marbles in the bag.

  10/30 = 1/3, so C is the right answer.  

You can rule out other choices by repeating the above steps and substituting appropriate values