ISSB Academic & Intelligence Test Mathematics: Averages MCQs

ISSB Academic & Intelligence Test Mathematics: Averages MCQs — sample questions

1. Question 1

   Q1. Average of 5 numbers is 20. If one number is removed, average becomes 18. The removed number is:

   • A) 24
   • B) 26
   • C) 28
   • D) 30

   Answer: 28

   Explanation: Sum of 5 = 100. Sum of 4 = 72. Removed = 100 − 72 = 28. Use totals, not averages, when numbers are added/removed.

2. Question 2

   Q2. Average of 5 numbers is 18. If one number 12 is replaced by 32, new average?

   • A) 20
   • B) 22
   • C) 24
   • D) 26

   Answer: 22

   Explanation: Sum was 90. New sum = 90 − 12 + 32 = 110. Average = 110/5 = 22.

3. Question 3

   Q3. Average of first five natural numbers?

   • A) 2
   • B) 3
   • C) 4
   • D) 5

   Answer: 3

   Explanation: Sum 1+2+3+4+5 = 15. Divide by 5 gives 3. Work each step carefully; ISSB math rewards accuracy under time pressure.

4. Question 4

   Q4. The average of five test scores is 20. If four scores are 15, 18, 22, and 25, what is the fifth score?

   • A) 20
   • B) 18
   • C) 22
   • D) 24

   Answer: 20

   Explanation: Five numbers with average 20 have a total of 100. The four given scores sum to 80, so the fifth score is 20.

5. Question 5

   Q5. A naval training march covers 120 km in 2 hours. What is the average speed?

   • A) 60 km/h
   • B) 40 km/h
   • C) 80 km/h
   • D) 100 km/h

   Answer: 60 km/h

   Explanation: Average speed equals total distance divided by total time. One hundred twenty divided by 2 gives 60 km/h.

6. Question 6

   Q6. The average of eight numbers is 12. If the number 20 is replaced by 8, what is the new average?

   • A) 11
   • B) 10.5
   • C) 12.5
   • D) 9.5

   Answer: 10.5

   Explanation: The original total is 96. Replacing 20 with 8 lowers the total by 12 to 84. The new average is 84 divided by 8, which is 10.5.

7. Question 7

   Q7. What is the average of the first 10 natural numbers?

   • A) 5
   • B) 5.5
   • C) 6
   • D) 4.5

   Answer: 5.5

   Explanation: The first 10 natural numbers sum to 55. Dividing by 10 gives an average of 5.5.

8. Question 8

   Q8. The average of 12, 18, 24, and 30 is:

   • A) 18
   • B) 20
   • C) 21
   • D) 24

   Answer: 21

   Explanation: Sum is 12 plus 18 plus 24 plus 30, which equals 84. Average is 84 divided by 4, which is 21.

9. Question 9

   Q9. The average of five numbers is 28. If one number 40 is removed, what is the average of the remaining four?

   • A) 20
   • B) 24
   • C) 25
   • D) 26

   Answer: 25

   Explanation: Total of five numbers is 140. After removing 40, the sum is 100. Average of four is 100 divided by 4, which is 25.

10. Question 10

    Q10. The average of 5, 7, 9, and 11 is:

    • A) 7
    • B) 8
    • C) 9
    • D) 10

    Answer: 8

    Explanation: Sum is 32 and there are 4 numbers. Average is 32 divided by 4, which is 8.

11. Question 11

    Q11. Average of 10 numbers is 20. If one number 30 is replaced by 40, new average is:

    • A) 20
    • B) 21
    • C) 22
    • D) 19

    Answer: 21

    Explanation: Total was 200. Replacing 30 with 40 adds 10, so total becomes 210. Average is 21.

12. Question 12

    Q12. Average of 10, 20, 30, 40 is:

    • A) 20
    • B) 25
    • C) 30
    • D) 35

    Answer: 25

    Explanation: Sum is 100 and count is 4. Average is 25. Work each step carefully; ISSB math rewards accuracy under time pressure.

13. Question 13

    Q13. Average of five numbers is 20. Their sum is:

    • A) 80
    • B) 100
    • C) 120
    • D) 90

    Answer: 100

    Explanation: Sum equals average times count. 20 times 5 equals 100. Work each step carefully; ISSB math rewards accuracy under time pressure.

14. Question 14

    Q14. Average of 6, 8, x is 9. What is x?

    • A) 11
    • B) 12
    • C) 13
    • D) 14

    Answer: 13

    Explanation: Sum of three numbers is 27. 6 plus 8 plus x equals 27, so x is 13.

15. Question 15

    Q15. Average of 4, 8, 12, 16 is:

    • A) 8
    • B) 10
    • C) 12
    • D) 14

    Answer: 10

    Explanation: Sum is 40 and count is 4. Average is 40 divided by 4, which is 10.

16. Question 16

    Q16. Average of 5 numbers is 12. Sum is:

    • A) 50
    • B) 60
    • C) 55
    • D) 65

    Answer: 60

    Explanation: Sum equals average times count. 12 times 5 equals 60. Work each step carefully; ISSB math rewards accuracy under time pressure.

17. Question 17

    Q17. Average of 7, 9, x is 10. x is:

    • A) 12
    • B) 14
    • C) 16
    • D) 18

    Answer: 14

    Explanation: Sum of three numbers is 30. 7 plus 9 plus x equals 30, so x is 14.

18. Question 18

    Q18. Average of first 5 odd numbers is:

    • A) 3
    • B) 5
    • C) 7
    • D) 9

    Answer: 5

    Explanation: First five odd numbers sum to 25. Average is 5. Work each step carefully; ISSB math rewards accuracy under time pressure.

19. Question 19

    Q19. Average of 5, 15, 25 is:

    • A) 10
    • B) 15
    • C) 20
    • D) 25

    Answer: 15

    Explanation: Sum is 45 and count is 3. Average is 15. Work each step carefully; ISSB math rewards accuracy under time pressure.

20. Question 20

    Q20. Average of 8 numbers is 15. Sum:

    • A) 100
    • B) 120
    • C) 130
    • D) 140

    Answer: 120

    Explanation: Sum equals average times count. 15 times 8 equals 120. Work each step carefully; ISSB math rewards accuracy under time pressure.