If a merchant offers a discount of 40% on the marked price of his goods and thus ends up selling at cost price, what was the % mark up?
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If SP = CP, then the discount fraction must balance the markup fraction. A discount of 40% (\( 2/5 \)) on MP means SP is \( 3/5 \) of MP. Therefore, MP is \( 5/3 \) of SP (and CP). \( 5/3 = 1 + 2/3 \), so the markup is \( 2/3 \) or 66.66%.