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Plugging In: Invisible Plugging In - Percents

A retail store decreased the price of a dinner set by 10% during a summer sale. The price of the set was further reduced by 20% in a clearance sale. If Donna uses a 5% discount coupon to buy the dinner set during the clearance sale, what percent of the original price of the dinner set does she pay?
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Correct. [[snippet]] __Plug In__ 100 for the price of the dinner set (the invisible variable). After the summer sale, the price of the set will be 10% less (i.e., $90). A further 20% reduction is >$$90\times \frac{20}{100} = 18$$, thus $$90-18=72$$ is the clearance sale price. Donna gets another 5% discount on that price. Did you accurately calculate the price Donna paid for the dinner set?
There is no need to go through needless, tedious calculations if you can quickly and easily __Ballpark__, especially in percent problems. Use the 10% block to guess for Donna's 5% discount. Since 10% of 72 is 7.2, half of that is 5% (i.e.,3.5). So Donna paid approximately $$72-3.5=68.5$$ for the dinner set. There is no need in further calculations for Donna's percentage since you wisely __Plugged In__ 100.
Sure, I did.
No, I didn't. There was no need.