please solve the fifth word problem

[barbie]

Karen purchased a prepaid phone card for
$20
. Long distance calls cost
11
cents a minute using this card. Karen used her card only once to make a long distance call. If the remaining credit on her card is
$17.47
, how many minutes did her call last?

 

[math_celebrity]

Find what was used:
Used Money = Prepaid original cost - Remaining Credit
Used Money = 20 - 17.47
Used Money = 2.53

Using (m) as the number of minutes, we have the following cost equation:
C(m) = 0.11m

C(m) = 2.53, so we have:
0.11m = 2.53

Divide each side by 0.11
m = 23