Question 607312
Your notion that there is a formula for the solution of such problems is wrong.


What we do is we express the given information as a simple algebraic equation with one unknown figure ( In this case the no of pages of smaller type. Note that once you know the pages of smaller type then the pages with large type is 21 less that no )


We denote no of small type pages by x representing a no and the equation turns out to be 


 x * 2400 + (21-x) * 1800 = 48000 which we obtain by simply adding the words in all 21 pages assuming small type page no to be x.

progressively simplifying above equation we have 
2400x + 21 * 1800 - 1800x = 48000
i.e. 600x = 48000 - 21 * 1800 = 48000 - 37800 = 10200
i.e. x = 17

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