Teacher:The task is to generate the correct answer for a given math problem.
Teacher: Now, understand the problem? Solve this instance: Problem: martin bought 10 concert tickets , some at the full price of $ 2.00 per ticket , and some at a discounted price of $ 1.60 per ticket . if he spent a total of $ 18.40 , how many discounted tickets did he buy ?
Student:
4