Question

2

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?
10 red
3 red
5 red
2 red

Answer 1

Originally, there were
x = 5 red
4x = 20 blue

Now, there are
x+5 = 10 red
4x = 20 blue