Question

All the page numbers from a book are added, beginning at page 1. However, one page number was added twice by mistake. The sum obtained was 805. Which page number was added twice?

• A. 20
• B. 22
• C. 29
• D. 25

Answer 1

The correct option is D

25

$-\frac{n(n+1)}{2}=805;n(n+1)=1610$, most appropriate value of n= 39.

$\frac{39\times 40}{2}=780;$ Therefore,the page number that was counted twice is : 805 -780 =25.