The average of the marks of 25 students in a class is 19. Later, the teacher realized that the marks of two students were taken as 18 and 19 respectively, instead of 14 and 15. Find the new actual average marks of the class.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 18.68.
We know that,
Average = Sum of observations/Number of observations
Now,
Total marks of 25 students with wrong numbers = 25 × 19 = 475
Correct total = 475 - (18 + 19) + (14 + 15)
⇒ 475 - 37 + 29 = 467
New average = 467/25 = 18.68
Hence, the new actual average mark of the class is 18.68