Scores on a test have a mean of 66 and Q3 is 80. The scores have a distribution that is approximately normal. Find the standard deviation. Round your answer to the nearest tenth.

18.7
20.9
10.5
9.4

Question

Scores on a test have a mean of 66 and Q3 is 80. The scores have a distribution that is approximately normal. Find the standard deviation. Round your answer to the nearest tenth.
 	
	18.7
	20.9
	10.5
	9.4

amistre64 · Answer

well, what would you say the range is?

anonymous · Answer

My answer is A

amistre64 · Answer

it may be, but i havent determined it yet,  what is your approach?

amistre64 · Answer

Q3 means that 75% if the data falls under 80,  with a mean of 66

do we find a z score associated with .7500 ?  how do we approach this?

anonymous · Answer

idk i am confused

amistre64 · Answer

well, you picked A, why?  is it just your favorite letter?

amistre64 · Answer

you either have a table of z scores to work with, or a stats calculator

amistre64 · Answer

ti83 maybe?

anonymous · Answer

no I just re did it and I got 10.5

amistre64 · Answer

what did you 'redo' ... you havent given me anything to assess here.

anonymous · Answer

i did 80 - 16 and i got 14 then i did 14 x 0.7500 and I got 10.5

amistre64 · Answer

ok, thats something to work with.

14 is good.

do you know this formula?

$$z=\frac{x-\mu}{\sigma}$$

amistre64 · Answer

also, looking at a rough sketch of what we are looking for

|dw:1432091128344:dw|

there is no simple way to guess at the value of z, it has to be tabled up, or calculatored.