The seller made a profit selling 100 oranges for 300 dollars.

So each orange selling price was 3 dollars.

Now, these 3 dollars are already the final price via wich the merchant made a profit. so the cost price of one orange is 3 minus some buck.

If I bought an orange at 2,80 dollars and sell it at 3 dollars my gain is 0.2 dollars. This is basic accountability.

Quantity A says the % of profit which is our 0.2 dollars of difference called as X so \(\frac{x}{3}\)

Quantity B says the selling price expressed as % of the cost price. So \(\frac{x}{3-x}\)

Now \(\frac{x}{3} = \frac{x}{3-x}\)

Clearly, B is bigger because the fraction is smaller

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