



 
With problems like this, I do not begin with a rule (though I can create one after analysis) but with a picture, really a small scale simulation. What if the numbers were smaller? If I start on page 3, and end on page 5, how many pages I have read? I imagine the pages Part of the difficulty is that we are not quite reading the whole page (and turning each page). Similarly, if I need to end at the bottom of page 4, then I might start turning from the bottom of page 2 (top of page 3) in order to cover two pages. Alternatively, I might turn page 4 (looking at the top of page 5) so 2 pages starts at the top of page 3. You are actually trying to count 'whole pages'  but the words suggest an imaginary set up with is not quite complete! Therefore the numbers 'slip' and subtraction/ addition do not quite fit. You will see I am using visual thinking  but in a way that only some features matter, and I could imagine the picture with pages 99, 100, Walter Whiteley  


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