Which are 15% off?
680 to 578
1120 to 896
340 to 289
250 to 212.50

Answers:
680 to 578
340 to 289
250 to 212.50

Reasoning:
To find the percent of a number:
If the percentage is less than 100, we place a decimal point in front of the percent. Then, we multiply the percent by the whole.
For example, .15 x 680 = 102. Since 15% is less than 100, we place a decimal point in front of the 15. Then, we just multiplied it by the whole of 680.

We know that 102 = 15% of 680, so since that is the amount of money taken off the total, we subtract it: 680-102=578. Therefore, the new price is 578.

I did this for the rest of the questions, and there are 3 correct answers:
680 to 578
340 to 289
250 to 212.50