Challenge 172: Flipping Fortune
How likely am I to save 20p or less?
I have a collection of five coins: one 1p, one 2p, one 10p, one 20p and one 50p.
They are all fair coins, equally likely to show heads or tails.
I toss all the coins simultaneously and put any that come up tails in my savings jar.
What is the probability that I save 20p or less?
(You should assume that no coins land on their edge!)