Q19 of 43 Page 296

Three numbers are chosen from 1 to 20. Find the probability that they are not consecutive

Since, the set of three consecutive numbers from 1 to 20 are (1, 2, 3), (2, 3, 4), (3, 4, 5), ..., (18,19,20)

Considering 3 numbers as a single digit


∴ the numbers will be 18


Now, we have to choose 3 numbers out of 20. This can be done in 20C3 ways


∴ n(S) = 20C3


The desired event is that the 3 numbers are choose must consecutive. So,











Hence, the correct option is (B).

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(a) An odd number appears in a single toss of a fair die.


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(c) A king, 9 of hearts, or 3 of spades appears in drawing a single card from a well shuffled ordinary deck of 52 cards.


(d) The sum of 6 appears in a single toss of a pair of fair dice.

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