Answer:
28 bags but see below
Explanation:
Start by subtracting 320 from 1700
1700 - 320 = 1680
Now he can buy any number of bags as long as he doesn't go over 1680 pounds. Let's see what that means
1680 / 60 = 28 bags of cement.
The answer to the math problem is 28 bags.
In real life, you likely want to trim it that close. What if you hit a bump. That would be very hard on the springs. I'd drop it down to 26 bags if I was actually transporting concreate mix.
He could by any number of bags between 1 and 28 in a math class and a few less in actual practice.