this one should be ``` .scan(String::length) .reduce(0)... ``` not ``` .map(String::length) .reduce(0) ``` here is url: https://thomasnield.gitbooks.io/rxjavafx-guide/content/2.%20RxJava%20Fundamentals.html#scan and here is a screenshot 
this one should be
not
here is url: https://thomasnield.gitbooks.io/rxjavafx-guide/content/2.%20RxJava%20Fundamentals.html#scan
and here is a screenshot