1. The average of 20 numbers is zero. Of them, how many may be greater than zero, at the most?
2. The average of five consecutive odd numbers is 25. What is the product of the largest and smallest numbers?
3. The average of 10 numbers is 6. If each number is multiplied by 4, what will be the new average?
4. The average age of a family of 6 members is 30 years. If the youngest member is 6 years old, what was the average age of the family just before the youngest member was born?
5. The average of 7 numbers is 28. If one number is excluded, the average of the remaining numbers is 26. What is the excluded number?
6. The average of 15 results is 75. If the average of the first 8 results is 70 and that of the last 8 results is 80, what will be the 8th result?
7. The average weight of 8 persons increases by 2.5 kg when a new person replaces one of them weighing 65 kg. What is the weight of the new person?
8. The average of 9 numbers is 20. If the average of the first 5 numbers is 15 and the average of the last 5 numbers is 25, find the 5th number.
9. The average score of 25 students in a class is 84. The highest score is 97 and the lowest score is 59. If the highest and lowest scores are excluded, what will be the new average score?
10. The average salary of 100 employees in an office is $500 per month. If the average salary of 30 employees is $400 per month and that of another 20 employees is $600 per month, what is the average salary of the remaining 50 employees?