Multiple choice

The average mark scored by 50 students in a class was calculated to be 38. Later it was found that marks of two students were wrongly copied as 34 and 23 instead of 43 and 32. Find the correct average mark.

  1. 37.36

  2. 39.00

  3. 38.36

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Initial sum = 50 * 38 = 1900. Error: 34 and 23 were added instead of 43 and 32. Difference = (43 + 32) - (34 + 23) = 75 - 57 = 18. Correct sum = 1900 + 18 = 1918. Correct average = 1918 / 50 = 38.36.

AI explanation

The correct total marks can be found by adjusting the original sum for the errors using the net change in marks. The correct marks of 43 and 32 total 75, while the wrongly copied marks of 34 and 23 total 57, meaning the total marks were underestimated by 18. Because the average was calculated based on 50 students, this 18 mark increase must be divided by 50, which gives an average increase of 0.36. Adding this 0.36 increase to the original average of 38 yields the correct average mark of 38.36.

Keep practicing — related questions