Average:

1. Q: Find the average of 10, 20, 30.
   Answer: (10+20+30)/3=20 

2. Q: The average of 5, 15, 25, 35 is?
   Answer: (5+15+25+35)/4=20

3. Q: Average of first 5 natural numbers?
   Answer: (1+2+3+4+5)/5=3

4. Q: Average of first 10 even numbers?
   Answer: (2+4+...+20)/10=11

5. Q: Average of first 10 odd numbers?
   Answer: (1+3+...+19)/10=10

6. Q: The average of 7 numbers is 15. Their sum is?
   Answer: 15\times 7=105 

7. Q: The average of 20 numbers is 25. If one number is removed, average becomes 24. Find the removed number.
   Answer: Removed number = (20\times 25)-(19\times 24)=500-456=44

8. Q: The average of 5 numbers is 18. If one number is 30, find the average of the remaining 4.
   Answer: Sum = 5\times 18=90. Remaining sum = 90-30=60. Average = 60/4=15

9. Q: The average of 4 numbers is 20. If one number is 10, find the average of the remaining 3.
   Answer: Sum = 80. Remaining sum = 70. Average = 70/3\approx 23.33

10. Q: The average of 6 numbers is 12. If one number is 18, find the average of the remaining 5.
    Answer: Sum = 72. Remaining sum = 54. Average = 54/5=10.8

11. Q: The average age of 30 students is 15 years. If teacher’s age is included, average becomes 16. Find teacher’s age.
    Answer: Teacher’s age = (31\times 16)-(30\times 15)=496-450=46 

12. Q: The average weight of 40 students is 50 kg. If teacher’s weight is included, average becomes 51. Find teacher’s weight.
    Answer: Teacher’s weight = (41\times 51)-(40\times 50)=2091-2000=91

13. Q: The average marks of 50 students is 60. If one student’s marks are wrongly entered as 80 instead of 50, find correct average.
    Answer: Wrong sum = 3000. Correct sum = 3000-80+50=2970. Correct average = 2970/50=59.4

14. Q: The average of 10 numbers is 25. If each number is increased by 5, new average is?
    Answer: 25+5=30

15. Q: The average of 8 numbers is 20. If each number is doubled, new average is?
    Answer: 20\times 2=40

16. Q: The average of 3 consecutive even numbers is 18. Find the numbers.
    Answer: Numbers = 16, 18, 20 

17. Q: The average of 5 consecutive odd numbers is 25. Find the numbers.
    Answer: Numbers = 21, 23, 25, 27, 29

18. Q: The average of 4 consecutive multiples of 7 is 35. Find the numbers.
    Answer: Numbers = 21, 28, 35, 42

19. Q: The average of 100 natural numbers is?
    Answer: (1+100)/2=50.5

20. Q: The average of first 50 odd numbers is?
    Answer: (1+99)/2=50