Finding the number of beads with given probability

Question

20 beads are in a bag.Some are green and some are red.The chance that one bead taken from the bag at random is red is 1/4.How many red beads are in the bag?

Answer 1

Let the number of red beads be r. Since there are 20 beads in all, the probability of picking a red one from amongst them at random is r / 20, which is also 1 / 4. You can now solve for r.