Mock AIME 2 Pre 2005 Problems/Problem 4
Problem
Let . Given that
has
digits, how many elements of
begin with the digit
?
Solution
Note that has the same number of digits as
if and only if
has a leading digit
. Therefore, there are
numbers with leading digit
among the set
However,
also starts with
, so the answer is
.
See also
Mock AIME 2 Pre 2005 (Problems, Source) | ||
Preceded by Problem 3 |
Followed by Problem 5 | |
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