Amovie streaming website charges an initial fee of $50, plus $5 for each movie that is streamed. how many movies must be streamed for the average cost per movie to fall to $7?

The average cost of streaming N movies will be
.. average cost = (total cost)/(number of movies)
.. = (50 +5N)/N
.. = (50/N) +5

You want this value to be 7, so you have
.. 7 = (50/N) +5
.. 2 = 50/N
.. N = 50/2 = 25

25 movies must be streamed to get the average cost down to $7.

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