2001 AIME I Problems/Problem 1
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Problem
Find the sum of all positive two-digit integers that are divisible by each of their digits.
Solution
Let our number be 
, 
. Then we have two conditions: 
and 
, or 
divides into 
and divides into 
. Thus 
or 
(note that if 
, then would not be a digit).
- For
, we have 
for nine possibilities, giving us a sum of 
.
- For
, we have 
for four possibilities (the higher ones give 
), giving us a sum of 
.
- For
, we have 
for one possibility (again, higher ones give ), giving us a sum of 
.
If we ignore the case 
as we have been doing so far, then the sum is 
.
Using casework, we can list out all of these numbers: 
.
See also
| 2001 AIME I (Problems • Resources) | ||
| Preceded by First Question | Followed by Problem 2 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
