Work done so far....
If X ~ N(22,4), z = (x - 22)/sqrt(4) ~ N(0,1) Thus, P(20 <= X <= 21) = P((22-20)/2 <= z <= (22-21)/2) = P(1<= z <= 0.5) = P(z <= 1) - P(Z <= 0.5) Now, we use the table above. P(z <= 1) - P(Z <= 0.5) = 0.8413-0.6915=0.1463
Is it correct?