Thread: Hi, I'm a new user, and I need help with this Statistics problem

1. Hi, I'm a new user, and I need help with this Statistics problem

Hi! This seems like a great place and everyone is so helpful sand I need some help so I came here. I'm in AP Statistics and this problem has me confused.
So, here is the problem-

Suppose 75% of all families spend more than $75 weekly for food, while 15% spend more than$150. Assuming the distribution of family expenditures on groceries is normal, what is the mean weekly expenditure and standard deviation?

I have no idea how to start it or anything, thanks for the help guys!

2. Re: Hi, I'm a new user, and I need help with this Statistics problem

Originally Posted by datpinecone
Hi! This seems like a great place and everyone is so helpful sand I need some help so I came here. I'm in AP Statistics and this problem has me confused.
So, here is the problem-

Suppose 75% of all families spend more than $75 weekly for food, while 15% spend more than$150. Assuming the distribution of family expenditures on groceries is normal, what is the mean weekly expenditure and standard deviation?

I have no idea how to start it or anything, thanks for the help guys!
From a table of cumulative values for the standardised normal distribution, you can find out what 'score' encompassed 75% of the area from the right and what score encompasses 15% of the area from the right.

Then you can use the formula for standardising the normal distribution $Z = \frac{X - \mu}{\sigma}$. Simultaneous equations.