Explanation:
Let's assume that Mandy had x appointments in one day.
According to the problem statement, she charges $78 per appointment, so the total amount earned from appointments can be represented as 78x.
She also earned $90 in tips, so the total amount earned in the day can be represented as 78x + 90.
We know that the total amount earned in the day was $480, so we can set up the equation:
78x + 90 = 480
Subtracting 90 from both sides gives:
78x = 390
Dividing both sides by 78 gives:
x = 5
Therefore, Mandy had 5 appointments in one day.