A bag contains counters that are red, blue, green or yellow. The number of counters are 9 which is red, 3x is blue, x-5 is green, 2x is yellow. A counter is chosen at random. The probability it is red is 9/100. Work out the probability it is green.

So as there are 9 reds, you know that the total number of counters is 100 (because red probability is 9/100)

so you can work out x by writing an equation.

9 + 3x + x - 5 + 2x = 100

from here you can add up all of the x's and the numbers (so you have 3x+x + 2x = 6x) (and for numbers you have 9 and - 5, 9 - 5 = 4) so putting these together you have 6x and 4 you get the following:

6x + 4 = 100

take away 4 from both sides

6x = 96

divide both sides by 6

x = 96/6 = 16

green is x-5 so if you substitute the result we got for x ...

16-5 = 11. so there are 11 greens

therefore the probability would be 11/100 as there are 100 counters overall.