A bag contains n counters.

One counter is blue and the rest are red.

Two counters are taken at random from the bag.

a) Express, in terms of n, the probability that a counter of each colour is

Give your answer as a fraction in its simplest form.

b) The probability that a counter of each colour is taken is 0.125

How many red counters are in the bag?

Blue

1 / n

Red

n-1 / n = 1 - 1 / n

7 red containers

Step-by-step explanation:

If there are "n" counters in total but we know that one is blue it means that there are "n - 1" red counters, which means that the probability for when one of them is:

Blue

1 / n

Red

n-1 / n = 1 - 1 / n

for part b, we have that the probability is 0.125, that is:

1 / n = 0.125

if we solve for n:

n = 1 / 0.125

n = 8

knowing that of the 8 one is blue, it means that the rest are red, that is to say that there are 7 (8 - 1) red containers