What is the probability of a quarter?

Answer 1

I'm assuming you are asking what is the probability (P) of flipping a quarter.

This answer really depends upon how many times up are going to flip it.

If you are flipping it once, you have a 50% chance that it will land on heads and a 50% chance that it will land on tails. Either way the sum of your probabilities will add up to 1, meaning that there is a 100% chance that something will occur (see probability rules).

EX: Let H= heads and let T=tails

∑P= P(H)+P(T)=0.5+0.5=1

However, let's say you were going to flip a coin 3 times and were wanting to know what the probability of getting at least 1 tail was. You would approach the problem this way:

P( at least 1 tail)=?

Next, you want to find the compliment (the opposite of what you are starting with). So the opposite of getting one tail is getting no tails. This is the same as getting all heads.

P(no tails)=P(all heads)

P( all heads)= P(H)3 Heads is cubed because you are flipping the coin 3

= P(0.5)3 times and want all the outcomes to be heads.

= 1/8

By knowing that the outcome plus its compliment add up to equal 1 you get:

P( all heads) + P( at least 1 tail)=1

P( at least 1 tail) = 1- P( all heads)

P( at least 1 tail) = 1- 1/8

P( at least 1 tail) = 7/8

So the probability of flipping a coin 3 times and getting a least 1 tail is 7/8. In other words, it's very likely that it will land on tails one of those three times.