# SAT Math Multiple Choice Practice Question 521: Answer and Explanation

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**Question: 521**

**20.** A store sells boxes of 6 lightbulbs for $30 each, and boxes of 12 lightbulbs for $48 each. The price per bulb is what percent less when purchased in a box of 12 than in a box of 6 ?

A. 80%

B. 75%

C. 50%

D. 25%

E. 20%

**Correct Answer:** E

**Explanation:**

**E** Let's start by finding the amount per bulb when bought in a pack of 6: If you can buy 6 bulbs for $30, then each bulb will cost $30 ÷ 6, or $5. In a box of 12, each bulb will cost $48 ÷ 12, or $4. Now you need to figure out the percentage difference between $5 and $4. The formula for percentage difference is . In this case, a reduction from $5 to $4 is a difference of $1 over an original price of $5. So the percentage difference is = 20%.