Question 8
The teacher writes all integers from 1 to 100 in the board. In how many ways can Lisa erase two numbers such that the sum of the remaining 98 numbers is an even number?
**Editorial note for this self-study exercise:** Count each unordered pair of distinct erased numbers once; changing the order of erasing the same two numbers does not make a new way.
**Editorial note for this self-study exercise:** Count each unordered pair of distinct erased numbers once; changing the order of erasing the same two numbers does not make a new way.