6. (10 points) Use 40 yuan to buy three types of exercise books priced at 2 yuan, 5 yuan, and 11 yuan each. You must buy at least one of each type, and the money must be exactly spent. How many different ways are there to buy the exercise books? $\qquad$ kinds.
【Analysis】Subtract 1 from each type, leaving $40-2-5-11=22$ yuan. Then, based on the remaining money, classify and solve the problem.

【Solution】Solution: Subtract 1 from each type, leaving $40-2-5-11=22$ yuan. If you buy 2 more 11-yuan books, it will be exactly used up, counting 1 method; If you buy 1 more 11-yuan book, 11 yuan remains, you can buy 1 5-yuan book and 3 2-yuan books, counting 1 method; If you do not buy any more 11-yuan books, with 22 yuan, you can buy at most 4 5-yuan books, the number of 5-yuan books can be $4,2,0$, counting 3 methods. In total, there are $1+1+3=5$ methods.

Answer: There are 5 different purchasing methods.