Probability qn 1
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The probability that a number selected at random between 100 and 999 (both inclusive) will not contain the digit 7 is: (a)16/25 (b)(9/10)^3 (c)27/75 (d)18/25

Solution

First digit can be chosen in 8 ways from 1-9 excluding 7
Second digit in 9 ways from 0-9 excluding 7 and third digit also in 9 ways.
So, total no. of ways excluding 7 = 8*9*9
Total no. of ways including 7 = 9 * 10 * 10
So, ans = (8*9*9)/(9*10*10) = 18/25




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The probability that a number selected at random between 100 and 999 (both inclusive) will not contain the digit 7 is: (a)16/25 (b)(9/10)^3 (c)27/75 (d)18/25

Solution[edit]

First digit can be chosen in 8 ways from 1-9 excluding 7
Second digit in 9 ways from 0-9 excluding 7 and third digit also in 9 ways.
So, total no. of ways excluding 7 = 8*9*9
Total no. of ways including 7 = 9 * 10 * 10
So, ans = (8*9*9)/(9*10*10) = 18/25