Question

Took purchased a prepaid phone card for $20. Long distance calls cost 7 cents a minute using this card. Yoko used her card only once to make a long distance call. If the remaining credit on her card is $15.92, how many minutes did her call last?

Answer 1

To find this answer you must first set up an equation, and to do that you must identify your constant values and unknown values. We know that she paid a flat fee of $20 for her card so that is the constant value. We do not, however know how many minutes she spent on her long distance call so that could be the variable x. We also know that the 7 cents directly relates to minutes. That leaves us with the equation:
15.92 = 20 - .07x

Now, to solve this, you want to isolate x. to start, you can subtract 20 from each side to isolate -.07x. That leaves you with the equation of:
-4.08 = -.07x

Lastly, just divide each side by -.07 to completely isolate x. That should give you an answer of x = 58.29 minutes. Hope this helps! Let me know if you still have any questions about this.