The task is to generate the correct answer for a given math problem.

[Q]: Problem: a dishonest dealer professes to sell goods at the cost price but uses a weight of 800 grams per kg , what is his percent ?
[A]: 25 %

[Q]: Problem: company c sells a line of 20 products with an average retail price of $ 1,200 . if none of these products sells for less than $ 400 , and exactly 10 of the products sell for less than $ 1,000 , what is the greatest possible selling price of the most expensive product ?
[A]: 11000

[Q]: Problem: the average of first six prime numbers greater than 20 is ?
[A]:
3