Answer: 15
Step-by-step explanation:
Given : Level of confidence = 0.90
Significance level : [tex]\alpha=1-0.90=0.10[/tex]
Critical value : [tex]z_{\alpha/2}=1.645[/tex]
Margin of error : [tex]E=\text{ 3 dollars}[/tex]
Standard deviation: [tex]\sigma=\text{ 7 dollars}[/tex]
The formula to find the sample size : [tex]n=(\dfrac{\sigma\times z_{\alpha/2}}{E})^2[/tex]
[tex]\Rightarrow n=(\dfrac{7\times(1.645)}{3})^2=14.7328027778\approx15[/tex]
Hence, the minimum sample size needed= 15.
