Question 93553
Let C be the original cost that the appliance store paid for the microwave. Since the markup
rate is 30% (or 0.30 in decimal form) of the original cost you can tell that after the markup
the customer who buys the microwave will be expected to pay to the appliance store the original
cost plus the markup.  Therefore, the customer will pay C + 0.30*C. But the problem 
tells you that this amount is $300.00. So you can write the equation that:
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{{{C + 0.30C = 300}}}
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On the left side the two terms add to give:
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{{{1.3C = 300}}}
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Then you can solve for C by dividing both sides of this equation by 1.3 to get:
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{{{(1.3C)/1.3 = 300/1.3}}}
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On the left side the 1.3 in the numerator cancels with the 1.3 in the denominator
and you are left with just C. On the right side you divide 300 by 1.3 and get $230.769
which rounds to $230.77.
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So the store paid $230.77 for the microwave. The 30% markup was 0.30 times $230.77 
which is $69.23. And the cost to the customer is the sum of these two which is:
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{{{230.77 + 69.23 = 300.00}}}
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Everything works out so the answer checks.
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Hope this helps you to understand the problem a little better.