Final answer:
The price of the sweater was reduced by 40%.
Step-by-step explanation:
To calculate the percentage by which the price of the sweater was reduced, we need to find the difference between the original price and the new price, and then divide it by the original price.
The original price of the jeans was $30, and the new price is $18. The difference is $30 - $18 = $12.
To find the percentage, we divide the difference by the original price and multiply by 100. Percentage reduction = ($12 / $30) x 100 = 40%.