Question

The average amount of money spent per day by students in
Mrs. Ross’s class for lunch is $2. In this class, 90% of students spend less than
what amount per day?

Answer 1

90% of the class could spend 1c, the other 10% could spend enormous amounts and the average could still be $2. This question is stupid.

Answer 2

I don't get it

Answer 3

Don't worry, me either. Silly question.

Answer 4

The amount would be 1.28 standard deviations above $2.

Answer 5

bme89, can you explain more .Please!

Answer 6

How you get 1.28 standard deviations

Answer 7

The standard deviation will depend on the data set

Answer 8

Yeah, if you assume a normal distribution, you can look it up in a z table
http://www.sjsu.edu/faculty/gerstman/EpiInfo/z-table.htm
What you do is search the table for the value closest to .9, and then add the row title to the column title which will yield the number of standard deviations from the mean.
So this means that 90% of the normal distribution will be in the range of -infinity $ to $2 + 1.28 standard deviations.

Answer 9

look up on the row titles 1.2 then follow the row across to the column titled 0.08 The value in that cell is .8997 which is the closest value to .9 in the table.

Answer 10

,this question doen't give data set, I don't know how to find mean, standard deviation ?
you said 90% is mean?

Answer 11

The mean is at 50%. If you add 1.28 standard deviations to the mean, you will be at 90%.

Answer 12

I still dont see 1.28 at table?

Answer 13

There isn't a cell with 1.28 in it. You hunt the table for the value closest to .9, then add the row title to the column title of that cell (1.2+0.08=1.28)

Answer 14

I attach file , can you look the graph and tell me what number I fill the on the graph ?

Answer 15

start midle 50%
and what mean nmuber ?

Answer 16

Your mean is $2. The percents shown in on the graph indicates the percent amount of the data set that are within that interval. Since we are trying to find the price at which 90% of the students purchase their lunch, then we start at the left of the graph and add the percents until we get to 90% (0.5 + 2 + 13.5 + 34 ....etc.) We can simply start at the mean with 50% because 0.5+2+13.5+34=50. The difficulty is that by adding, you cannot get exactly at 90%. This is why we look up the value in the Z table. We find that if we move 1.28 standard deviations above the mean, then 90% of the data will lie below that point.

Answer 17

ty

Answer 18

No problem. Does this make sense?

Answer 19

yes

Answer 20

great