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M01 10 Vs M09 17

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M01 10 Vs M09 17 [#permalink] New post 11 Sep 2009, 13:30
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Both these questions are similar but the answers are contradicting.

M01-10 says there are 20 7's from 1 to 100 (using single/double/triple digit approach), whereas M09-17 says there are 19 9's from 1 to 100. Any single digit except 0 will appear 19 times from 1 to 99 !!

Or am I missing something?
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Re: M01 10 Vs M09 17 [#permalink] New post 11 Sep 2009, 16:15
Economist wrote:
Both these questions are similar but the answers are contradicting.

M01-10 says there are 20 7's from 1 to 100 (using single/double/triple digit approach), whereas M09-17 says there are 19 9's from 1 to 100. Any single digit except 0 will appear 19 times from 1 to 99 !!

Or am I missing something?


7, 17, 27, 37, 47, 57, 67, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 87, and 97 - total 20.
9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, and 99 - total 20.
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Re: M01 10 Vs M09 17 [#permalink] New post 23 Sep 2009, 05:53
I think you misunderstood what m09-17 meant. The question in m09-17 is as follows:

Quote:
All pages of a book are numbered. If the first page is numbered 1 and the last page is numbered 705, on how many pages does digit 9 appear in the numeration?


Here's a piece from the m09-17 OE:

Quote:
In the first 100 we have 10 pages where 9 appears as a units digit and 10 pages where 9 appears as a tens digit. Page 99 is counted twice, so the total number of pages on which 9 appears in the first 100 is 19.


So, OE doesn't say there are 19 9's from 1 to 100. It is saying that there are 19 pages where a 9 appears. The page numbered "99" should be counted only once since the question asks for "the number of pages where digit 9 appears". Whereas 99 contains two 9 digits, we add only one page to the count.

Hope it helps.

Economist wrote:
Both these questions are similar but the answers are contradicting.

M01-10 says there are 20 7's from 1 to 100 (using single/double/triple digit approach), whereas M09-17 says there are 19 9's from 1 to 100. Any single digit except 0 will appear 19 times from 1 to 99 !!

Or am I missing something?

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Re: M01 10 Vs M09 17   [#permalink] 23 Sep 2009, 05:53
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