You pay $2.40 for 3/4 pound of grapes. Your friend buys a pound of grapes at the same time and estimates that he will pay $1.80. What can you say about your friend's estimate?

My friend is right because $2.40 ÷ 4 = $0.60, and
$0.60 • 3 = $1.80.

My friend has to pay less than $1.80 because grapes cost only 80 cents per pound.

My friend has to pay more than $1.80 because I pay more than that for a smaller number of grapes!

The problem does not give enough information for me to judge if my friend is right.

Question

You pay $2.40 for 3/4 pound of grapes. Your friend buys a pound of grapes at the same time and estimates that he will pay $1.80. What can you say about your friend's estimate?

My friend is right because $2.40 ÷ 4 = $0.60, and 
$0.60 • 3 = $1.80.

My friend has to pay less than $1.80 because grapes cost only 80 cents per pound.

My friend has to pay more than $1.80 because I pay more than that for a smaller number of grapes!

The problem does not give enough information for me to judge if my friend is right.