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'At Least One...' printed from http://nrich.maths.org/
Imagine flipping a coin three times.
What's the probability you will get a head on at least one
of the flips?
Charlie drew a tree diagram to help him to work it out:
He put a tick by all the outcomes that included at least one
How could Charlie use his tree diagram to work out the probability
of getting at least one
How could he use it to work out the probability of getting no
What do you notice about these two probabilities?
Devise a quick way of working out the probability of getting at least one
you flip a coin 4, 5, 6... times.
What is the probability of getting at least one
you flip a coin ten times?
Once you've worked out a neat strategy for the coins problem, take
a look at these related questions which can be solved in a similar
Imagine choosing a ball from this bag and then replacing it.
If you did this three times, what's the probability that you
would pick at least one
What if you didn't replace the ball each time?
Imagine a class with 15 girls and 13 boys.
Three children are chosen at random to represent the class at
What is the probability that there will be at least one
Why not try the problem Same Number!