Problem:
How many integers in the set have the property that the sum of the decimal digits of is even?
, 2014
Solution
Solution:
Answer: 201
We know that 2014 does not qualify the property. So, we'll consider instead. Now, we partition this set into 2 sets: and .
For each, the first and second set are basically and , where , respectively. And we know that for each value of , must be either even or odd, which makes exactly one of have even sum of decimal digits. Therefore, there are in total 201 such numbers.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.