Mingmai recently purchased a set of premium wireless earbuds with a charging case for $37.99. He purchased this item at one of the local big-box department stores in Huntsville, Alabama where the sales tax rate at the time of purchase was 9.25%.

1. Suppose he had access to an electronic coupon on his smartphone for 20% off the retail price. What would Mingmai total cost be, including sales tax?
2. Mingmai assumed that her final total cost would be 10.75% less than the original retail price.
   1. Consider the coupon and sales tax and explain why he may have deduced this.
   2. Before calculating, guess. Do you think Mingmai assumption is correct? Why?
   3. Then, calculate. Now what do you think about Mingmais assumption? Support your answer with a detailed mathematical explanation.