To determine the charge per minute, we can use the two points provided: (0, 15) and (50, 90).
Step 1: Identify the points
- The first point (0, 15) means that when no minutes are used, the total charge is $15, which is the flat fee.
- The second point (50, 90) means that when 50 minutes are used, the total charge is $90.
Step 2: Set up the equations We can express the total charge \( C \) as: \[ C = F + r \cdot m \] where:
- \( C \) = total charge
- \( F \) = flat fee (which we know is $15 from the first point)
- \( r \) = charge per minute (which we need to find)
- \( m \) = number of minutes
From the first point (0, 15): \[ 15 = F \]
From the second point (50, 90): \[ 90 = F + r \cdot 50 \]
Step 3: Substitute \( F \) into the second equation Now, substitute \( F = 15 \): \[ 90 = 15 + r \cdot 50 \]
Step 4: Solve for \( r \) \[ 90 - 15 = r \cdot 50 \] \[ 75 = r \cdot 50 \] \[ r = \frac{75}{50} \] \[ r = 1.5 \]
Thus, the charge per minute is \( r = 1.5 \).
Final Answer: The charge per minute is $1.50.
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