3. If x is the greatest four- digit number such that the sum of the digits is 23 and no two digit are the same, which of the following is NOT a digit of x?
4. On a 200 question test the total score is the number of questions correctly minus 1/5th of the total number of questions answered incorrectly or left unanswered. What is the minimum number of questions that must be answered correctly to receive a total score of at least 100?
7. In stack A, invoices are assigned consecutive numbers, beginning with 1. In stack B, invoices are assigned consecutive odd numbers, beginning with 1. In stack C, invoices are assigned consecutive multiples of 3. If there are 25 invoices in each of these stacks, how many assigned
numbers are common to all three stacks?
8. If the sum of all the positive divisors of an integer n is equal to 2n, then n is called a perfect number. Which of the following is a perfect number?