Answer
See below.
Work Step by Step
a) The mean of $n$ numbers is the sum of the numbers divided by $n$.
Hence the mean: $\frac{2.25+3.50+2.75+3.10+1.90 }{5}=2.7$
b) The deviation is the difference of the data item and the mean.
Hence here the deviations: $2.25-2.7=-0.45,3.5-2.7=0.8,2.75-2.7=0.05,3.1-2.7=0.4,1.9-2.7=-0.8$
c) The sums of the deviations: $-0.45+0.8+0.05+0.4-0.8=0$
