To determine for which amounts of monthly phone use Plan A costs less than Plan B, we need to compare the costs of the two plans based on the number of minutes of phone use (m).
First, let's set up the equation to represent the cost of Plan A:
Cost of Plan A = $38 (monthly fee) + 4 cents per minute of use = 38 + 0.04m
Next, let's set up the equation to represent the cost of Plan B:
Cost of Plan B = $20 (monthly fee) + 7 cents per minute of use = 20 + 0.07m
To find out when Plan A costs less than Plan B, we need to set up an inequality. Since we want Plan A to cost less, we'll use the "less than" symbol (<).
38 + 0.04m < 20 + 0.07m
Now, we can solve the inequality for m to find the range of monthly phone use where Plan A costs less than Plan B.
Let's start by isolating the variables on one side of the inequality:
38 - 20 < 0.07m - 0.04m
Now simplify the inequality:
18 < 0.03m
Divide both sides of the inequality by 0.03 to isolate m:
18/0.03 < m
Simplify the division:
600 < m
So, the inequality is m > 600.
Therefore, for any amount of monthly phone use (m) greater than 600 minutes, Plan A will cost less than Plan B.