GCSE Maths revision · Probability and statistics
On a tree diagram, multiply along the branches for 'and', and add the end results for 'or'. Without replacement, the second set of branches changes because there is one fewer item.
Watch out Without replacement, take one off the total (and off that colour) for the second pick.
The probability that it rains on any day is 0.3. Assume the weather on Monday and on Tuesday is independent.
(a) Work out the probability that it rains on both days.
(b) Work out the probability that it rains on neither day.
Answer (a) 0.09; (b) 0.49
A bag contains 2 blue counters and 5 white counters. A counter is taken at random, replaced, and then another counter is taken at random. Work out the probability that both counters are blue. Give a fraction in its simplest form.
A bag contains 5 red counters and 3 blue counters. Two counters are taken at random, one after the other, without replacement.
Work out the probability that both counters are the same colour.
A box contains 4 green balls and 6 yellow balls. Three balls are taken at random without replacement.
Work out the probability that at least one of the balls is green.
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