Question 1202746
t, original number of books
0.4t were fiction
0.6t were nonfiction

875, number of borrowed books
n+f=875
n=875-f


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When 875 books were borrowed, the number of fiction books became half of the original 
number and the number of non-fiction books were decreased by 25%.
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That seems to say, "the number of fiction books became HALF of the original number of 
the fiction books,..."


{{{system(0.4t-f=(0.5)(0.4)t,0.6t-(875-f)=(0.75)(0.6)t)}}}


{{{system(0.4t-f=0.2t,0.6t+f-875=0.45t)}}}


{{{system(0.2t=f,0.15t+f=875)}}}


{{{substitution_for_f}}}, {{{0.15t+0.2t=875}}}

{{{0.35t=875}}}

{{{highlight_green(t=2500)}}}, the original total number of books before some were checked-out or removed

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