Question

A medical devices company wants to know the number of hours its MRI machines are used per day. A previous study found a standard deviation of six hours. How many MRI machines must the company find data for in order to have a margin of error of at most 0.70 hour when calculating a 98% confidence interval

Answer 1

The company has to study 199 machines.

In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.

It is given that;

Margin of error E = 0.7

Confidence interval 98% = 1-0.98 = 0.02

Standard deviation = 6 hours

Number of MRI machines needed per day n, = [(z alpha/2 * SD)/E]²

Z alpha/2 = 1.645 at alpha = 0.1

Inputting these values into n we have that

[(1.645*6)/0.7]²

= 14.1²

= 198.81 is approximately equal to 199

The company has to study 199 machines.

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