Vinod wanted to read a story book which contains 3 pages. He read 1 page on the first day, 2 pages on the second day, 3 pages on the third day and so on. How many days it took for Vinod to complete the book?

Options

A. 12 days
B. 18 days
C. 30 days
D. 24 days

Answer

D

Explanation

Let the number of days taken to complete the book = n days.
According to the question
`1 + 2 + 3 + ....n = 300` or `(n(n+1))/2 = 300`
`[because " Sum of first n natural numbers i.e. "1 + 2 + ... +n = (n(n + 1))/2]`
or `n (n + 1) = 600 `
or, `n (n + 1) = 24 xx 25 `
or, `n = 24 `
So, the number of days taken to complete the book = n days = 24 days.