When the number of storybooks decreases by 100 and the number of science and technology books increases by 100 (the result of the second case), there are five storybooks,1/this storybook, that is, the number of storybooks in this case is 5/(1/kloc-0).
Storybook increased by 500, science and technology book decreased by 500 (the result of the first case), storybook 1 book, science and technology book 3. In this case, the story book accounts for1/(1+3) =1/4;
Comparing the two cases, 5/ 16 is greater than 1/4 (100+400)=500, that is, 500 is the total (5/16-1/4) =/kloc-.
So the total is 500/(116) = 8000.
The number of story books is 8000 * (1/4)-400 =1600.
The general idea is that there are 400 storybooks less than the total 1/4 and more than the total116 100.