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Solutions
Given,
The average marks of 45 students was 70 for a unit test:
Average marks = Total marks of students/Number of students
Total marks of all 45 students = 70 × 45 = 3150
Total marks of all 45 students = 3150
Given,
It was noticed that 20th roll number student marks which is 45 was wrongly taken as 60:
Total sum of marks of 44 students = Total sum of 45 students - 60
= 3150 - 60 = 3090
∴ Total sum of marks of 44 students is 3090.
New total sum of marks of 45 students = 3090 + 45 = 3135
New total sum of marks of 45 students = 3135
New average = 3135/45 = 69.66
∴ The corrected new average marks is 69.66