Multiple choice

The average marks of students in a class of 20 students in Geography subject is 68. If the marks of two students were entered as 48 and 65 instead of the actual marks 72 and 61 respectively, find out the correct average of marks if the error had not been made.

  1. 66

  2. 68

  3. 69

  4. 71
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Initial sum = 20 * 68 = 1360. Correct sum = 1360 - 48 - 65 + 72 + 61 = 1380. Correct average = 1380 / 20 = 69.

AI explanation

The total error in the sum is calculated by finding the difference between the actual marks and the incorrect marks: (72 + 61) - (48 + 65) = 133 - 113 = 20. Because the actual marks are higher, the total sum increases by 20, making the increase in the average 20 / 20 = 1. Add this 1 to the incorrect average of 68 to find the correct average of 69.

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