A Methods and Measurements Analyst for Digital Devices Needs to Develop

Multiple Choice

A methods and measurements analyst for Digital Devices needs to develop a time standard for the task of assembling a computer mouse. In a preliminary study, she observed one of her workers perform this task six times with the following results: $$\begin{array} { | l | c | c | c | c | c | c | } \hline \text { Observation } & 1 & 2 & 3 & 4 & 5 & 6 \\\hline \text { Time(Seconds) } & 46 & 38 & 40 & 34 & 42 & 40 \\\hline\end{array}$$ How many observations should be made if she wants to be 86.64 percent confident that the maximum error in the observed time is .5 second? Assume that the standard deviation of the task time is four seconds.

A)  10
B)  12
C)  120
D)  144
E)  169