There are some counters in a bag. The counters are red or white or blue or yellow. Bob is going to take at random a counter from the bag.
The table shows each of the probabilities that the counter will be blue or will be yellow.
Colour
red
white
blue
yellow
Probability
0.45
0.25
There are 18 blue counters in the bag.
The probability that the counter Bob takes will be redis twice the probability that the counter will
be white.
(a) Work out the number of red counters in the bag.