Answer:
A 10% sale means that the post-sale price of the item is now 90%, or 0.9 of the original cost of the item. We then apply 9% sales tax by multiplying the 0.9 by 109%, or 1.09. 0.9 * 1.09 = . 981, so the total cost of the item is 98.1% of the original pre-sale sticker price.
Explanation:
