Time management is very much important in IIT JAM. The eduncle test series for IIT JAM Mathematical Statistics helped me a lot in this portion. I am very thankful to the test series I bought from eduncle.
Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Rishab Soni Best Answer
The mean of 1/3 of the student is 60 = The mean of 1/3 of the students of 210 is 60 = The mean of 70 students is 60 = Total score of 60 students = 60 X 70 = 4200 (1) Total mean of rest (2/3) of the students = Total score of 140 students is 78 X 140 = 10920 Total Score of the group is (10920 + 4200) / 210 = 72. The mean of the whole group is 72.
To calculate the mean, we have formula Total Score / Toal number. We already have total number as 210. Now we need total score. For tha, the next info provided is 1/3 of students have mean of 60. Meaning total score of 70 students/70 is 60. To calculate total score of 70 students, we multiply 70 with 60 (number with mean) and we get 4200 (1), Repeating the same with the next data for remaining 140 students, we get the total score as 10920 (2) . Now we can calculate the total score by adding (1) and (2) which should give us 15120. Divide that with total number of students (210) and we'll get mean as 72.