The average marks of 25 students is 48. Later, 5 new students join the group, each scoring 60 marks. After that, the teacher finds that one of the original students' marks was wrongly entered as 40 instead of 70. Find the final average marks of the class.
Show answer & explanation
Correct answer: C
Explanation
Given:
Average of 25 students = 48
New students = 5 (each with 60 marks)
One student's marks were recorded as 40 instead of 70 (i.e., 30 less marks were recorded).
By the formula:
Average = Total Marks / Total Students
Total marks of 25 students = 25 × 48 = 1200
Correct marks should have been
= 1200 + (70 − 40)
= 1200 + 30
= 1230
Marks of 5 new students = 5 × 60 = 300
Total marks = 1230 + 300 = 1530
Total students = 25 + 5 = 30
Final average = 1530 / 30 = 51