Final answer:
The retailer plans to mark up the cell phone by 10%, which is $85. Therefore, the total amount of markup added to the cell phone is $85.
Step-by-step explanation:
A retailer purchases a cell phone for $850 and plans to markup the cost by 10%. The student has asked about the amount of markup a retailer would add to a cell phone purchased for $850 with a planned 10% markup. To calculate the amount of markup, you must first convert the percentage to a decimal. For 10%, this would be 0.10. Then, you multiply this decimal by the cost of the item:
$850 × 0.10 = $85
Therefore, the amount of markup on the cell phone is $85. This means the retailer will add $85 to the cost of the cell phone before selling it to the customer.