Statement 1:
To get a $3 fee, the first order's price must have been between less than $100. With no additional information, we can determine that (1) is insufficient since:
Scenario A: Order #1 has price $1, delivery fee $3. Order #2 has price $1, delivery fee $3.
Scenario B: Order #1 has price $1, delivery fee $3. Order #2 has price $1,000, delivery fee $7
Both scenarios respect the delivery cost schedule and statement (1). However while in Scenario A the sum of prices is tiny, in Scenario B the sum of prices is greater than $499.
[spoiler](1) is not sufficient.[/spoiler]
Statement 2:
To determine sufficiency, do your best to answer the question in multiple ways without contradicting the statement. If multiple answers are achievable, you have insufficiency.
Scenario A: make the sum of prices large. The easiest way to get $10 total delivery fee is to have one order with a $3 fee and another with a $7 fee. This will allow us to avoid that big nasty fraction. This is easy: Order #1 has price $1, delivery fee $3. Order #2 has price $1,000 delivery fee $7. Sum of fees is $10 and sum of prices is greater than $499.
Scenario B: make the sum of prices small (hopefully smaller than $499). To make prices small while keeping delivery fees high (equal to $10), need to take advantage of the first tier since for very low prices, delivery is expensive (relative to order price). So we could have order #1 price $0.01 and delivery fee $3. However to get to $10 total delivery fee, we must either have a order #2 with price > 500 (delivery fee would be $7 taking total delivery to $10) or make Order #2 price = 500 (delivery fee from the middle tier would be 3+(500-100)/100 = $7, taking total delivery to $10). Either way, the total order price has to be greater than $499.
[spoiler](2) is sufficient.[/spoiler]
B is correct.
