Ben bought 7 notebooks for $34.50. some of the notebooks were $3.50 each and the others were $4.25 each. if x represents the number of least expensive notebooks, which equation can be used to find the number of least expensive notebooks purchased?

There are two types of notebooks which Ben bought. One type cost $ 3.50 each and the other type cost $4.25 each. The number of least expensive notebooks is x. This means Ben bought x notebooks of $ 3.50 each.

Since he bought 7 notebooks in total, the number of other notebooks will be
(7 - x)

The price of 7 notebooks was $34.50. So we can set up the equation as follows:

3.50x + 4.25(7 - x) = 34.50

Using this equation we can find the value of x i.e. the number of least expensive notebooks purchased.