17. The store purchased a batch of footballs at a wholesale price of 30 yuan each and sold them at a retail price of 45 yuan each. When there were still 30 footballs left, the store had already made a profit of 1500 yuan. How many footballs did the store purchase?
【Solution】Method 1: After the remaining 30 footballs are sold, the store makes a total profit of $1500+30 \times 45=2850$ yuan. Each football makes a profit of 15 yuan, so a total of $2850 \div(45-30)=190$ footballs were purchased. Method 2: Let the number of footballs purchased be $x$.
According to the problem, we have $45(x-30)=30 x+1500 \Rightarrow x=190$