The average marks obtained by a class in an examination were calculated as 30.8. However, while checking the marks entered, the teacher found that the marks of one student were entered incorrectly as 24 instead of 42. After correcting the marks, the average becomes 31.4.
How many students does the class have?
A.
25
B.
28
C.
30
D.
32
Solution:
m observations avg is pm, but there is wrong observation instead of correct observation then
original avg is = mp – wrong + correct / m
m[30.8]-24+42 / m = 31.4
m(30.8) + 18 = (31.4) m
18 = m (31.4 – 30.8)
Then m = 30.