Gary bought an MP3 player at a 20% discount sale for $52. What was the original price of the MP3 player?

100 - 20 = 80%

$52 represents 80% of the original price of the MP3 player.

13 represents 20% of the original price of the MP3 player.

13 * 5 = $65

20 * 5 = 100%

The original price of the MP3 player was $65.

Check:

65 * 0.2 = 13

65 - 13 = 52