GED Math: Probability

Hey, yo, all, probability is the sweetest part of math. Tells you how likely something is to happen. And here’s a probability question from Zaher:

If Rob flips 3 coins what is the chance that they will come up all tails?

The correct answer was : 1/8 , but it doesn’t make sense to me ! can you explain why it is 1/8 ?

First things first. To find the probability of ONE thing happening, you’ve got to figure out how many times the thing you’re asking about will happen, and put that over how many times anything will happen. Flipping a coin is pretty easy. It could come up heads, or it could come up tails. There are two possibilities, and one chance that it’ll come up tails one out of two.

Probability of tails on one coin flip = 1/2

That’s the total number of possibilities it’ll come up tails over the total number of possibilities, altogether. Got it?

Now, you’ve got to figure out, separately, the probability that it’ll come up tails EACH of the three times. That’s simple. They’re all the same. The chance is 1/2 that it’ll come up tails each time you flip the coin. So you got three 1-in-2 chances.

First try: 1/2

Second try: 1/2

Third try: 1/2

How do you figure out what the odds are of it coming up tails all three times? Multiply! Remember, to multiply fractions, multiply all the top numbers to get the top number and multiply all the bottom numbers to get the bottom number:

1/2 × 1/2 × 1/2 = 1/8

There’s 1/8 chance of it coming up tails three times in a row.

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