boxing506 wrote:

Can somebody explain? I think I did not get the question.

The question askes you to select a 3 digit number. So we need to selct 3 digits from {1, 2, 3, 4, 5, 6, 7, 8, 9}.

Now number of ways we can select 1 digits = 9. Since there are 9 options to choose from!

Now number of ways we can select 3 digits =

9 \times 9 \times 9 = 729Now the above section contains digits like = 999, 888, 777 ..... they are not allowed (3-digit integers with all alike digits )

So correct answer is

729 - 9 = 720. Hence B.

_________________

Sandy

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