Normal Distribution

#1
I cant figure out how to do this problem: I have 2 sets of means and 2 sets of SD

1sth graders scored a mean of 25 and a sd of 5
5th graders scored a mean of 30 and an sd of 10; assume the distributions are normal

How do i figure out what percentage of the first graders scored better than the average 5th graders?

i did (30-25)/5 which gives me 1; the z-score percentile i get is 15.57% (smaller portion) but i dont think thats how you do it.

The second question asks which percentage of fifth graders scored lower than the average 1st grader. But I will end up getting the same answer if i do it the same...
 

Dason

Ambassador to the humans
#2
the z-score percentile i get is 15.57% (smaller portion) but i dont think thats how you do it.
Seems fine to me
The second question asks which percentage of fifth graders scored lower than the average 1st grader. But I will end up getting the same answer if i do it the same...
Will you? Give it a try.
 

Dason

Ambassador to the humans
#4
No. I'm saying do the actual calculation for the second one. Like forget about anything to do with the first problem and do the second problem.
 

Dason

Ambassador to the humans
#6
so would it be (25-30)/10? which would give me -.50 which is .3825?
Well -.50 isn't .3825. Be careful when you say stuff like this - it will cause graders to want to take away all of your points. Also that isn't the correct probability calculation even though it's the correct z-value.
 
#7
Well -.50 isn't .3825. Be careful when you say stuff like this - it will cause graders to want to take away all of your points. Also that isn't the correct probability calculation even though it's the correct z-value.
what would the correct probability be? I thought it would be 38.25% since that is one of the tails and I want to look at the percentage of students that scored lower than 25. Or most likely im seeing/understanding it wrong...any guidance?