Tiffany pays $40 for 160 minutes of talk time on her cell phone. how many minutes of talk time does she get per dollar?

$40 ... 160 minutes
$1 ... x minutes = ?

If you would like to know how many minutes of talk time does Tiffany get per dollar, you can calculate this using the following steps:

40 * x = 1 * 160
40 * x = 160    /40
x = 160 / 40
x = 4 minutes

Result: Tiffany gets 4 minutes of talk time per dollar.