(ii) If the number of students using no book at all is 10, and the number of students using all the three is 20. Show that the information is inconsistent.

A survey of 400 students in a university shows that 100 are smokers and 150 as chewers of gum, 75 are both smokers and gum chewers. Find out how many students are neither smokers nor gum chewers.