Normal probability density functions are bell-shaped and symmetrical around their means. (a) Write a script to generate and plot normal pdfs with μ = 0 and different o values of 0.5, 1 and 2 on the same graph. Provide the graph with a legend label. (b) Calculate the probability or area under each curve for the following values: ± 1 sd. (i) (ii) ± 2 sd. (iii) ± 3 sd. What can you conclude from the probability values obtained in (i) — (iii)?