Stats; Standard Normal model, z-scores , proportions

aaabbbb

Hi there just wondering if anyone can help me with any of these questions ?

Pherekydes

Any attempts, OP?

In all of these Qs you should draw a diagram until you get used to them, and even then a diagram helps. Mark the mean and the SD on the diagram.

In Q1: Are you looking for a large or small value? Mark where Z= -0.5. Is the area to the left of it big or small? Now examine the values in the question. Pick the closest.

Q2-15: Mark where you think 12cm should be on the diagram. There is no need to calculate! Estimation will do fine. Now, what percentage is to the right of 12cm? Is it big or small?

Q2-16: Do the same with this question. The answer should nearly jump off the diagram!

Q3-15, 16, 17: Use the same method.

Q4-11: You can eliminate one answer immediately! Now, what proportion of a normal distribution lies one SD from the mean? What is half of this? Now try to match that with the figures given.

Q4-12: Use the same method. Note that σ² is given.

aaabbbb

Pherekydes wrote: »

Any attempts, OP?

In all of these Qs you should draw a diagram until you get used to them, and even then a diagram helps. Mark the mean and the SD on the diagram.

In Q1: Are you looking for a large or small value? Mark where Z= -0.5. Is the area to the left of it big or small? Now examine the values in the question. Pick the closest.

Q2-15: Mark where you think 12cm should be on the diagram. There is no need to calculate! Estimation will do fine. Now, what percentage is to the right of 12cm? Is it big or small?

Q2-16: Do the same with this question. The answer should nearly jump off the diagram!

Q3-15, 16, 17: Use the same method.

Q4-11: You can eliminate one answer immediately! Now, what proportion of a normal distribution lies one SD from the mean? What is half of this? Now try to match that with the figures given.

Q4-12: Use the same method. Note that σ² is given.

Countless ! My exam's tomorrow and my head is wrecked with the bloody things ! It's the one part of the course I just can't seem to grasp. Despite tormenting my lecturer over it !

For question one looking at it with fresher eyes than yesterday I was thinking :
Find z score for 0.5 which equals 0.6915 then since its a negative value subtract 1 from 0.6915 giving 0.3085 would that be right ?


How can you tell from just drawing the digram ?

I mean it could be any % after 12 ?

Pherekydes

aaabbbb wrote: »

For question one looking at it with fresher eyes than yesterday I was thinking :
Find z score for 0.5 which equals 0.6915 then since its a negative value subtract 1 from 0.6915 giving 0.3085 would that be right ?

Yes.

How can you tell from just drawing the digram ?

I mean it could be any % after 12 ?

Mark 10cm on the diagram. It coincides with the mean, right? Now mark +1 SD. This is equivalent to 11.5cm. Now, where does 12cm lie? What % lies to the right of 12cm? Hint: It's very small.