The store made a $50 x 30/100 = $<<50*30/100=15>>15 profit for selling it 30% above the cost.
So, the book was sold for $50 + $15 = $<<50+15=65>>65.
During a sale, the book’s selling price decreased by $65 x 10/100 = $<<65*10/100=6.50>>6.50.
So, the book was sold for $65 - $6.50 = $<<65-6.5=58.50>>58.50.
There was $58.50 - $50 = $<<58.5-50=8.50>>8.50 profit after the discount.
Therefore, the percent profit is $8.50/$50 x 100% = <<8.5/50*100=17>>17%.
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