# Not Sure how to even start this one

• October 8th 2012, 01:45 PM
Not Sure how to even start this one
The mean number of travel days per year for salespeople employed by hardware distributors needs to be estimated with a 98% degree of confidence. For a small pilot study the mean was 150 days and the standard deviation was 12 days. If the population mean is estimated within four days, how many salespeople should be sampled?
• October 8th 2012, 02:45 PM
MaxJasper
Re: Not Sure how to even start this one
m=150
s=12 =sample sd
$\sigma =s\sqrt{n}$ = population sd
$z_{.98}=2.3263$ two-sided normal distribution z-value

$-\sigma z_{.98}\leq m\pm 4\leq \sigma z_{.98}$

$m+4\leq s z_{.98}\sqrt{n}$

Solve to obtain:

n > 30