How to work out probability?

HELP!!
I've got a big maths test tommorow and most of the questions are probabilty.
WHAT IS IT? HOW DO I WORK IT OUT?
Thanks x x x

probability is how much you take from something , ex: you got 3 red cars, 7 blue and 2yellow
the question will be like - whats the probability that X will chose a yellow car so you will need to add all the answers 3+7+2=12 AND THEN WRITE THE ANSWER AS A FRACTION yelloow = 2 yellow that is a possibillity
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12 ( total)

Can you give me an example, please?

Probability is simply the chance that something will happen.

If you roll a 6-sided die, the chance (probability) of rolling a 5 is 1 out of 6 ALSO WRITTEN 1:6 OR 1/6 OR 16.66...% probability
With a deck of 52 playing cards, the probability of drawing an ace is 4 out of 52 OR 1 out of 13 OR 1/13 OR 7.69% probability
Now, what is the chance of drawing a red card from a deck of 52 cards?
Try to solve the question before you read any farther.

ifyousaidthattheprobabilitywasfiftypercentyouareright

Don't panic and Good Luck!!