Topics · Edexcel GCSE Maths (1MA1)
When the first counter is not put back, the second draw comes from a different bag. The tree has to show that.
A bag contains 5 red counters and 3 blue counters.
Kai takes a counter at random from the bag and does not replace it.
He then takes a second counter at random from the bag.
Work out the probability that both counters are the same colour.
See why
Kai took a red counter first. What is the probability that his second counter is red?
RRRRRBBB
Now a fresh one
A box contains 4 lemon sweets and 6 orange sweets.
Priya takes two sweets at random, one after the other, without replacement.
Work out the probability that at least one of the sweets is lemon.
Learn it properly
Where it comes up in the exam
- Specification P8: calculate the probability of independent and dependent combined events, including using tree diagrams.
- On both tiers. Higher adds conditional probability (P9).
- Without replacement, both the numerator and the denominator change on the second branch.