Final answer:
Ellen can purchase 20 lilies for $36.00 at a rate of $1.80 each, by dividing the total amount she has by the cost per lily.
Step-by-step explanation:
To calculate the number of lilies Ellen can purchase with $36.00 when each lily costs $1.80, you perform a division. You divide the total amount of money Ellen has by the price of one lily.
$36.00 รท $1.80 = 20 lilies.
This means Ellen can buy 20 lilies from the flower market with her $36.00, as each lily is priced at $1.80 and the division of the total money by the price per lily yields an integer number of lilies. It's important to note that this calculation assumes Ellen spends all her money on lilies and there are no taxes or additional fees involved in the purchase.