**Question **: A box contains tickets numbered from 1 to 20. Three tickets are drawn from the box with replacement. The probability that the largest number on the tickets is 7 is

(A) 2/19

(B) 7/20

(C) 1-\left( \dfrac{7}{20}\right) ^{3}

(D) none of these

**Answer **: option (D)

**Solution **:

Let X denote the largest number on the 3 tickets drawn

Then, P\left( X\leq 7\right) =\left( \dfrac{7}{20}\right) ^{3} and P\left( X\leq 6\right) =\left( \dfrac{6}{20}\right) ^{3}. Then the required probability is,

p( x= 7) =\left( \dfrac{7}{10}\right) ^{3}-\left( \dfrac{6}{20}\right) ^{3}.

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