If you count 1 to 100 how many 6s will you pass on the way?

This common question is ambiguous and needs more detail. Variations of the answer with explanations are below. The most commonly asked form of this question deals with 6's so that is what shall be used in my answer. (If you do not understand, replace the 6's in my answer with 9's.)

[Literal Sense]

1 is the answer because the actual number '6' (by itself) only occurs once.

[The Digit 6]

20 is the answer because, the digit 6 appears 20 times in this example:

6, 16, 26, 36, 46, 56, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 76, 86, 96

[The Number 6]

10 is the answer.

These would be the numbers in which '6' occurs:

6, 16, 26, 36, 46, 56, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 76, 86, 96

This is because one does not count the digits that represent values other than 6 (i.e. 60, 600, 6000, etc.). So, in this case, the digits with a strikethrough are uncounted. Simply, 6's are only counted in the ones place value.