A whole seller buys plastic lamps for $18 each and sells them for $30.60 What is the percent markup based on cost?

30.60 - 18 = 12.60

12.6 / 18 = 0.7 = 70%

To find the percent markup based on cost, we need to calculate the difference between the selling price and the cost price, and then express it as a percentage of the cost price.

First, let's calculate the difference between the selling price and the cost price:

Markup = Selling Price - Cost Price
Markup = $30.60 - $18
Markup = $12.60

Next, we can calculate the percent markup based on cost by dividing the markup by the cost price and multiplying by 100:

Percent Markup = (Markup / Cost Price) * 100
Percent Markup = ($12.60 / $18) * 100
Percent Markup = 70%

Therefore, the percent markup based on cost for the plastic lamps is 70%.