If you wish to<u> mentally estimate</u> the <u>total cost</u> of items, <u>rounding </u>off the items to the<u> nearest half dollar</u>, then you have to consider all five items separately.
Five items cost $1.85, $.98, $3.49, $9.78, and $6.18.
To get 4 or fewer correct, at least 2 answers have to be wrong. And the probability of that is: 3/4 x 3/4=9/16 1-9/16=probability that 4 or fewer are correct=7/16 ☺☺☺☺