Question

There are only red counters, blue counters, white counters and black counters in a bag.
The table shows the probability that a counter taken at random from the bag will be red
or blue.
Colour red blue white black
Probability 0.2 0.5
The number of white counters in the bag is the same as the number of black counters in
the bag.
Tania takes at random a counter from the bag.
(a) Work out the probability that Tania takes a white counter.