Based on careful work study in the Alex Company, the results shown in the following table have been

observed:

Element Observations $($minutes$)$ Performance rating $(\%)$

$12345$

Prepare daily report $3540334239120$

Photocopy results $1210361513110$

Label and package report $3355490$

Distribute reports $151821174585$

a$)$ Compute the normal time for each work element

b$)$ If the allowance for this type of work is $15\%,$ what is the standard time?

c$)$ How many observations are needed for a $95\%$ confidence level within $5\%$ accuracy?