In which page the bookmark is?
- This 3-acts opera could be done as a group activity:
- The teacher distributes books among students
- In pairs, one students put the bookmark in a page of one book and ask to guess the page. The only provided information is the total number of pages of the book.
- The take note of the answer and the page where the bookmark has put.
- Swap the roles.
- The best mean approximation wins
- The previous activity could be modified introducing measuring with ruler the position of the bookmark and the width of the book
- Posted on twitter 
 Bordoy, X. In which page the bookmark is? @Estimation180 #mtbos this is 3-act activity http://theque.somenxavier.xyz/content/3-acts/llibre-nombre-de-pagines.en/ …. 2016. https://twitter.com/somenxavier/status/720850261074321411.