The first joke book

Let the common divisor of the two methods be M (= 35+40+45+)...+A), and the second method reads n pages after m, then:

Type 1: total number of pages =( 15+20+25+30)+m+29.

Type II: Total number of pages =m+n+39

So (15+20+25+30)+m+29 = m+n+39, and the solution is n=80.

Because 80 can't be the sum of two neighbors (with a difference of 5) divisible by 5, it can be deduced that a=75.

Therefore, the total number of pages =15+20+25+...+75+29 =13 * (15+75)/2+29 = 585+29 = 614 pages.