Can Anyone Help someone out who is Really stupid at math (me),

The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 47 minutes of calls is $16.23 and the monthly cost for 69 minutes is $19.09. What is the monthly cost for 49 minutes of calls?


Thanks

(19.09 - 16.23) / (69 - 47) =
2.86 / 22 =
0.13

So minutes cost 13 cents each.

16.23 + (49 - 47) * 0.13 =
16.23 + 2 * 0.13 =
16.23 + 0.26 =
16.49

So 49 minutes cost $16.49.

*Edit*: MacMan is incorrect. That would only be the case if zero minutes cost $0.00. However, many long-distance plans have a base price, so even if no minutes are used, the plan costs something. Using MacMan's method, 69 minutes would cost $23.83, while the problem clearly states that 69 minutes cost $19.09. We can figure out the base price once we know the price per minute, calculated as I did above, is 13 cents. 47 minutes costs $16.23, so zero minutes costs $16.23 - 47 * 0.13, which is $10.12. Watch what happens when we add 13 cents per minute to the $10.12 base price, to find the cost of 47, 49, and 69 minutes:

$10.12 + 47 * 0.13 = $16.23
$10.12 + 49 * 0.13 = $16.49
$10.12 + 69 * 0.13 = $19.09

We get the prices that the problem states are correct for 47 and 69 minutes, which should give us confidence that our calculated price of $16.49 for 49 minutes is also correct.

$16.92. What you do it divide the number of minutes by the cost to find the cost per minute. Then multiply by the number of minutes.