WEBVTT
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A card is drawn from a deck of cards numbered one to 30.
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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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Here are 30 cards numbered one to 30.
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And we want to know the probability that it has a number which is not divisible by 10.
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So first, letâ€™s figure out which numbers are divisible by 10.
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10 obviously is.
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And then 10 also goes into 20 twice.
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And then it also goes into 30 three times.
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So there are three out of the 30 that are divisible by 10.
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So we need to take those three away because we want the ones that are not divisible by 10.
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So we could either count all of these, or to subtract three from 30 to get 27.
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So 27 of these numbers are not divisible by 10.
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So again, 27 out of the 30 are not divisible by 10.
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However, we need to reduce this.
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Both of these numbers can be reduced by three.
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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.