Find number of people who don't fulfill a criteria based on mean and standard deviation.

[NahomTeshome]

Hello, I have a question that I need help with solving:

25 families are asked about how many cars they own. Two families have 3 cars, and no families have more than three cars. The mean is 18/25 and the standard deviation is 24/25. Find the number of families who don't own any cars.

I am especially stuck on how to find this as I don't think it can be a continuous normal distribution because the possible range ends at 3 so it's not a bell curve.
If you could help me solve it and tell me how to do it that would be great!
Thanks,
Nahom

 

[anon_hedgepig]

This is more of a car counting question.
If the mean number of cars owned is 18/25, then how many cars do all 25 families own?

What happens if you account for the two families that own 3 cars? How many cars are there left (call that x)? What is x?
Now, you have 23 families with x number of cars. Knowing that the remaining families can have at most 2 cars, what are the ways to partition x into a sum of 1 and 2? What standard deviations do these partitions correspond to?

 

[Dr.Peterson]

Hello, I have a question that I need help with solving:

25 families are asked about how many cars they own. Two families have 3 cars, and no families have more than three cars. The mean is 18/25 and the standard deviation is 24/25. Find the number of families who don't own any cars.

I am especially stuck on how to find this as I don't think it can be a continuous normal distribution because the possible range ends at 3 so it's not a bell curve.

This is not about a distribution, but about calculating the population mean and standard deviation from the data.

Here are the data:

0 cars: x
1 car: y
2 cars: z
3 cars: 2

x+y+z=23

Now write an expression for the mean, in terms of these variables. That gives you a second equation.

Then do the same for the standard deviation. That will give you a third equation.

Now solve for x.