Posted by **Anonymous** on Friday, June 1, 2007 at 1:40pm.

Head lice can be a problem in classrooms. From the past experience, suppose it is predicted that 5% of the students will get lice if there are some reported cases. The health nurse checks 120 randomly chosen students and records the number of students that have head lice. What is the probability that exactly 6, 7, 8 students in the random sample have head ice?”

How would I do this question??

I presume you mean that there is a 5% chance that a student, drawn at random, will have lice.

You could solve this exactly as a combinatorial problem. The probability of seeing exactly 6 is:

(.95^114 * .05^6)*Z, where Z is 120!/(6!*114!) (where ! means factorial). Repeat for exactly 7 and exactly 8.

Or you could solve approximately and use the properties of a binominal distribution. Here, the expected mean is .05*120=6, the standard deviation is sqrt(120*.05*95)=2.37 So, 8 is .84 standard deviations away from the mean. Use a cumulative normal distribution table to find your probability. (But, I wouldnt use 8, I would use 8.5)

## Answer this Question

## Related Questions

- science - How bad are lice really for your health and can they cause any major ...
- Grammar - Mother wondered from __________ her children had gotten the head lice...
- Math - The table shows the number of classrooms needed for different numbers of ...
- English - I have to write my cure for an "ill" that plague teenagers. This one ...
- childcare - 14. Caregivers shouldn't allow dress-up play with hats when _______ ...
- Math - School A has 480 students and 16 classrooms. School b has 192 students ...
- math - (Mad +lice)+(equations + r +p - square)= decimal_______
- Math - School A has 480 students and 16 classrooms, School B has 192 students ...
- Ms.Sue - Yesterday I wasn't able to post so I here I am posting it today for you...
- math - (Math+lice)+ (equations+R+P- Square)= Decimal_______ I don't have a clue ...