A phone company has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone. If a customer uses 410410 minutes, the monthly cost will be \$71.50$71.50. If the customer uses 720720 minutes, the monthly cost will be \$118.00$118.00. Use your equation to find the total monthly cost if 687687 minutes are used.



Answer :

The required cost is $ 101.22.

This problem can be solved by unitary method.

Given that monthly cost of customer if he uses 410 minutes is $71.

So, cost per minute = [tex]\frac{71}{410}[/tex]

                               =$ 0.17

And if the customer uses 720 minutes then the cost is $118.

So, cost per minute is = [tex]\frac{118}{720}[/tex]

                                   =0.16

Now if he uses 687 minutes then for 410 minutes cost incurred will be

= 410 × 0.17

= $ 69.7

And for next 197 minutes cost incurred will be = 197 × 0.16

                                                                         = $ 31.52

Total cost for 687 minutes = $(69.7 + 31.52)

                                         = $ 101.22

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