Out of a total of 9 books arranged in a particular order, the mean of the number of pages in the first 5 books is 430, the mean of the number of pages in the last 5 books is 380 and the mean of the number of pages in all the 9 books is 400. Find the number of pages in the fifth book.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e 450
the mean number of pages in the first 5 books is 430. total number of pages in the first 5 books = 430 x 5
= 2150 Eq....(i)
the mean number of pages in the last 5 books is 380.
total number of pages in the last 5 books = 380 x 5
= 1900 Eq....(ii)
the mean of the number of pages in all 9 books is 400.
total number of pages in all 9 books = 400 x 9
= 3600 Eq....(iii)
Number of pages in the fifth book Eq. (i)+Eq. (ii)-Eq. (iii)
= 2150+1900-3600
= 4050-3600
= 450