-According to Internet Statistics, the average American Facebook user spends app

Question

-According to Internet Statistics, the average American Facebook user spends approximately an average of 7 hours a month on the Facebook site. Assume the amount of user time on the Facebook site can be approximated by a normal distribution with hours per month and hours per month. Determine the percentage of Facebook users who spend:
-Less than 8.5 hours per month on the site?
-At least 4.5 hours per month on the site?
-Either less than 4.5 hours or more than 10 hours on the site?
-At most 390 minutes on the site? (Hint: Be careful with the unit in this question. You have to convert minutes to hours first)

Explanation / Answer

Ans:

Given that

µ = 7 hours per month and = 1.65 hours per month

1)

z=(8.5-7)/1.65=0.91

P(X<8.5)=P(z<=0.91)=0.8186

2)

z=(4.5-7)/1.65=-1.52

P(x>=4.5)=P(z>=-1.52)=1-P(z<=-1.52)=1-0.0643=0.9357

3)

z=(10-7)/1.65=1.82

P(x<4.5 or x>10)=P(z<-1.52 or z>1.82)=P(z<-1.52)+P(z>1.82)=0.0643+0.0344=0.0987

4) 390 min=390/60=6.5 hrs

z=(6.5-7)/1.65=-0.303

P(z<=-0.303)=0.3809

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