# Video: Determining the Probability of Compound Events

A card is drawn from a deck of cards numbered from 1 to 30. If a card is chosen at random, what is the probability that it has a number which is NOT divisible by 10?

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### Video Transcript

A card is drawn from a deck of cards numbered one to 30. If a card is chosen at random, what is the probability that it has a number which is not divisible by 10?

Here are 30 cards numbered one to 30. And we want to know the probability that it has a number which is not divisible by 10. So first, let’s figure out which numbers are divisible by 10.

10 obviously is. And then 10 also goes into 20 twice. And then it also goes into 30 three times. So there are three out of the 30 that are divisible by 10. So we need to take those three away because we want the ones that are not divisible by 10.

So we could either count all of these, or to subtract three from 30 to get 27. So 27 of these numbers are not divisible by 10. So again, 27 out of the 30 are not divisible by 10. However, we need to reduce this. Both of these numbers can be reduced by three.

Therefore, if a card is chosen at random, the probability that it has a number which is not divisible by 10 would be nine-tenths.