Mathematics for IGCSE & O level - Probability (Section 5 - No. 3)
Basma picks two pens at random. The bag contains 3 red pens and 5 blue pens. Which is the correct way to find the probability that Basma picks at least one blue pen?
Use a tree diagram to show the various combinations.
Calculate the probability of not picking a blue pen at all (both pens are red) and subtract from 1.
Add the probabilities of picking one blue and one red pen to the probability of picking two blue pens.
Multiply the probability of picking a blue pen by itself, since both picks are blue
Shpjegimi
The easiest way is to calculate the complement.