Answer:
(3 oz ; 4oz)
Explanation:
Given that :
Mean = 3.5 oz
Standard deviation = 0.5 oz
According to the empirical rule ; 68% is 1 standard deviation from the mean.
Hence, the interval that would represent the middle 68% will be:
(3.5 oz - 0.5 oz) ; (3.5 oz + 0.5oz)
(3 oz ; 4oz)