Part a
Find out the mean
mean=(2.55+3.10+2.65+2.45+3.25)/5
mean=14/5
mean=2.80
Part b
the deviation for each data
(2.55-2.80)=-0.25
(3.10-2.80)=0.30
(2.65-2.80)=-0.15
(2.45-2.80)=-0.35
(3.25-2.80)=0.45
Part c
The sum of the deviations is
(-0.25+0.30-0.15-0.35+0.45)=0