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Teresa purchased a prepald phone card for $20. Long distance calls cost 22 cents a minute using this card. Teresa used her card only once to make a long distance call. If the remaining credit on her card is $10.10, how many minutes did her call last?

Answer 1

#45#

The initial credit is #20#, the final credit is #10.10#. This means that the money spent can be found via subtraction:

#20-10.10 = 9.90#

Now, if each minute costs #0.22# it means that after #m# minutes you will have spent #0.22\cdot t# dollars. But you already know how much you spent, so

#0.22\cdot t= 9.90#

Solve for #t# dividing both sides by #0.22#:

#t = 9.90/0.22 = 45#

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.