Question 1
Source instructions: Answer all 10 questions and show detailed solutions. Each question is worth 4 points. Time limit:60 minutes.
The 400-digit number $12345678901234567890\ldots890$ is given.
Step 1: Cross out all the digits in odd-numbered places.
Step 2: Cross out all the digits in odd-numbered places of the remaining digits.
…
Continue until no digits remain. What is the last digit to be crossed out?
The 400-digit number $12345678901234567890\ldots890$ is given.
Step 1: Cross out all the digits in odd-numbered places.
Step 2: Cross out all the digits in odd-numbered places of the remaining digits.
…
Continue until no digits remain. What is the last digit to be crossed out?