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?

0.3\times 5,000=1,500

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.

\dfrac{1,500\text{ sheets}}{20\text{ minutes}}=75\text{ sheets per minute}

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.

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