Final answer:
By calculating the price per gallon for both Mary and Jill's purchases, it is found that Jill paid $2.40 per gallon while Mary paid $2.50 per gallon. Hence, Jill had the better buy.
Step-by-step explanation:
To determine who had the better buy between Mary and Jill, we need to calculate the price per gallon for each purchase. Mary bought 4 gallons of milk for $10.00, and Jill bought 2.5 gallons for $6.00.
For Mary, the price per gallon is calculated as follows:
$10.00 ÷ 4 gallons = $2.50 per gallon
For Jill, the price per gallon is calculated as:
$6.00 ÷ 2.5 gallons = $2.40 per gallon
Jill has the lower price per gallon, so Jill had the better buy.
Therefore, the answer is B) Jill.