The average marks of 39 students of a class is 50. The marks obtained by 40th student are 39 more than the average marks of all the 40 student are 39 more than the average marks of all the 40 students. Find the mean marks of all the 40 students.

Explanation

Let the mean marks of all the 40 students = `barX`
Given: `barX_(1)=50,N_(1)= 39`
Marks obtained by the 39 students
`sum X =50 xx 39 = 1,950`
Marks obtained by the 40th student
`= barX+39`
Mean marks of all the 40 students
` barX = (sumX)/N`
`barX= (1,950+barX+39)/40 `
`40 barX = 1,989 + barX`
`40 barX - barX = 1,989`
`39 barX = 1,989`
` barX = (1,989)/39 = 51 `
Thus, Mean marks of all the 40 students = 51.