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Bunuel
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The mistake I made on this problem was that I took (37.5% - 20%) / 20% = 17.5/20 = 87.5%. Can someone explain why this is not correct?

That's wrong because 37.5% and 20% are from different quantities.

Consider this, if biography books were 10% of 100 books and then became 50% of 1,000,000 books would it be correct to say that the increase in the number of biographies was (50-10)/10 = 400%?

Hope it's clear.

Hi Bunuel VeritasKarishma -

I also made the mistake and calculated the difference between 37.5 % and 20 % to get 17.5 % and calculated the resulting % change ( I ended up picking C incorrectly)

I now understand why my logic does not work because of the example posted in the purple font above

Can you provide a link / problem that flushes out this logic a bit more ?

While I have understood it, i want to perhaps read more about this logical fallacy or do some problems w.r.t this logical fallacy in order to imbibe it completely.
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Bunuel
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The mistake I made on this problem was that I took (37.5% - 20%) / 20% = 17.5/20 = 87.5%. Can someone explain why this is not correct?

That's wrong because 37.5% and 20% are from different quantities.

Consider this, if biography books were 10% of 100 books and then became 50% of 1,000,000 books would it be correct to say that the increase in the number of biographies was (50-10)/10 = 400%?

Hope it's clear.

Hi Bunuel VeritasKarishma -

I also made the mistake and calculated the difference between 37.5 % and 20 % to get 17.5 % and calculated the resulting % change ( I ended up picking C incorrectly)

I now understand why my logic does not work because of the example posted in the purple font above

Can you provide a link / problem that flushes out this logic a bit more ?

While I have understood it, i want to perhaps read more about this logical fallacy or do some problems w.r.t this logical fallacy in order to imbibe it completely.

Before you add/subtract percentages, you need to ensure that the bases of the percentages are the same.
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Hello from the GMAT Club BumpBot!

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