Keiko purchased a prepaid phone card for $20 . Long distance calls cost 16 cents a minute using this card. Keiko used her card only once to make a long distance call. If the remaining credit on her card is $17.28 , how many minutes did her call last?

17 minutes

Step-by-step explanation:

To answer this question, all we have to do is subtract the original amount of money on the phone card by what is remaining after Keiko's call:

20 - 17.28 = 2.72

Now, we divide this number by 0.16:

2.72 / 0.16 = 17

So, Keiko's call lasted 17 minutes

Hope this helps :)