Answer:
The convenience store has a markup amount of $30 on the pre-paid mobile phones and the retail price is $42
Step-by-step explanation:
The purchase price of the pre-paid mobile phones is $12.
The convenience store uses a markup rate of 250%.
The markup amount is:
250 * 12 / 100 = 30
The retail price is the purchase price plus the markup amount:
Retail price = $12 + $30 = $42
The convenience store has a markup amount of $30 on the pre-paid mobile phones and the retail price is $42
