Need some stats help!!!!

The size of the price discount offered by an industrial marketing manager varies according to order size. During the last quarter, the manager offered price discounts of 20% to one half of his customers and 30% to one-quarter of his customers, and no discount to the rest. He estimates that the probability of receiving a reorder this quarter is 0.90 if the customer received a 20% discount, 0.92 if the customer received a 30% discount, and 0.70 if the customer received no discount.

a) If a customer is selected at random and is observed not to have reordered, what is the probability that this customer was offered no discount last quarter?
b) If a customer is selected at random and is observed to have reordered, what is the probability that this customer was offered a 30% discount last quarter?

I know I am not presenting this in the right way (formula) but can someone tell me if the logic is flawed? This is for part a)

Discount # of Customers Reorder Will reorder Won't reorder
20% 50 90% 45 5
30% 25 92% 23 2
0% 25 70% 17.5 7.5


Probability randomly selected non reordering customer was offered no discount = 7.5%

 

Would b) just be 25 * .92 = 23%?

 

Okay, I get you, we're looking at the probability among non reordering customers not ALL of the customers.

Thanks!