Change $12\%$ into a decimal, and then combine it with the original $100\%$ of the value. What single decimal number can you multiply by 640 to get the new amount?

After you multiply 640 by your decimal, you may not get a whole number. How should you handle the decimal part when you are choosing from whole-number answer choices?

In Desmos, type 640*1.12 on a new line. Look at the numeric output Desmos gives; then decide which of the answer choices is closest to that value.

A 12% increase means you keep 100% of the original amount and add 12% more, for a total of $100\% + 12\% = 112\%$.

As a decimal, $112\% = 1.12$, so you can find the new amount by multiplying the original number by $1.12$.

Multiply the original number of laptops by this decimal:

Compute this product:

• $640 \times 1 = 640$
• $640 \times 0.12 = 76.8$

Add these: $640 + 76.8 = 716.8$.

So the exact increased amount is $716.8$ laptops.

You cannot sell a fraction of a laptop, so round $716.8$ to the nearest whole number, which is $717$.

Now compare $717$ to the answer choices: 670, 700, 720, and 760. The choice that is closest to $717$ is 720, so that is the correct answer.