Hi Mike! Can you please solve #29 (Test 8, Section 4)?

Thank you!

Sure thing! We know the machine starts with 5,000 sheets of paper, and has used 30% of that paper after 20 minutes. How much is 30% of 5,000?

It took 20 minutes to use 1,500 sheets, and we’re told the machine uses sheets *at a constant rate*, so we can calculate the rate of sheets per minute by dividing.

From there, we’ve got all the info we need to pick the right answer:

Translated, that just says the amount of paper left after *m* minutes is 5,000 (the amount of paper the machine began with) minus 75 (the number of sheets of paper used per minute) times *m*.

One last wonky note on this one: as soon as you see the part of the question that says the machine copies at a constant rate, you should eliminate choices C and D. Those are exponential functions, and “at a constant rate” means you need a linear function.