Question

Average of 17 students in a class is X. When their marks are arranged in ascending order it was found to be in arithmetic progression . The class teacher found that the ranked 15th, 11th, 9th, and 7th had copied the exam and hence they are suspended. Now the average of remaining class is y. Then

Answer 1

Explanation:

your complete question is ---> Average of 17 students in a class is X. When their marks are arranged in ascending order it was found to be in Arithmetic Progression. The class teacher found that rank the students who ranked 15th, 11th, 9th and 7th had copied the exam and hence they are suspended. Now the average of the remaining.

solution : marks of 17 students are in arithmetic progression.

i.e., a , (a + d), (a + 2d), (a + 3d) , ... (a + 16d)

so, average of marks of 17 students = sum of observations/number of observations

or, X = (17a + 8 × 17 d)/17

or, X = a + 8d

15th = (a + 14d), 11th = (a + 10d), 9th = (a + 8d ) and 7th = (a + 6d) are suspended.

so, average of remaining students, Y = {17a + 8 × 17d - (a + 14d) - (a + 10d) - (a+ 8d) - (a + 6d)}/13

Y = a + 7.5d

hence, Y < X