Bob has 120 beads
the beads are either red or green
bob gives 3/4 of the beads to his friend
2/3 of the beads bob now had are red
work out how many green beads bob now has

Bob has 10 green beads you can show this by dividing 120 by 4 and that then leaves 30 beads which is 1/4 of the original amount of beads. Now knowing that Bob has 30 beads you put it into an equation with x over 30 equal to 2/3 that then makes you able to see that if you multiple the denominator by 10 you get 30 so you do the same to the numerator causing x to be 20 and that is the amount of the red beads leaving 10 beads to be green.