The marks obtained by 40 students in class X of a certain school in a math paper of 100 marks total are presented in the table. Find the mean using direct method.
Class Interval0−1010−2020−3030−4040−50Number of students3413155
Class mark for first class interval = 5
Similarly the class mark for each class interval can be found. Look at the table.
Class IntervalNumber of students (fi) Classmark (xi) fixi 0−10351510−204156020−30132532530−40153552540−50545225Total∑fi=40∑fixi=1150
∴Mean=∑fixi∑fi
=5×3 + 15×4 + 25×13 + 35×15 + 45×540
=115040
=28.75