To find the percent decrease, we first need to find the amount of the decrease, which is the difference between the regular price and the sale price:
$550 - $456.50 = $93.50
So the amount of the decrease is $93.50.
To find the percent decrease, we divide the amount of the decrease by the original price and then multiply by 100:
($93.50 / $550) x 100 ≈ 17.0%
Therefore, the percent decrease of the sale price from the regular price is approximately 17.0%.