Annulus, Accuracy of Measurement and Normal Distribution - z score (1 Viewer)

[chickadee17]

hey

i have have a half yearly math exam on thursday, and im just studying for it.

I have come across Annulus, Accuracy of Measurement and Normal Distribution - z score, these three things have been giving me the shits, can anybody help me and explian how to work them out plz!!!!

Thanks

 

[cro_angel]

> annulus.. umm i forgot what it was all my maths stuff is at school but i think its an oval shape.. and the formula is pi times semi major and semi minor axis.. which is just like the 2 radius things.. if thats what i think it is.. its on the formula sheet and u just need to stick in numbers

> accuracy of measurement.. how accurate you are depends on the instrument you use.. for example using a 1m ruler to measure 2cm isnt as accurate as using a cm ruler.. and like when you measure something it lies between half plus minus of the smallest measurement.. eg if you use a mm ruler to get 10mm as a measurement.. the greatest possible error is plus or minus 0.5mm.. and sometimes you have to express the possible error as a % over the actual measurement...

z score- its basically how many SD's (standard deviations) away from the mean a score is.. when you are asked to find the z score they give u the mean and the SD.. today we had a question on the z score of 2 different test results and we had to say who did better (greater z score.. more numbers away from mean.. better..). with normal distribution.. u have to know that 68% of scores lie within 1SD, 95% lie within 2SD and 99.7% lie within 3SD.. like today they asked why might there be a problem with the machine if a screw with a diameter of 1.54cm is produced (when the mean is 1.5 and the SD is .01) and u gotta say that there is a 0.015% chance of it lying above 3SD.. thats basically how to apply it

 

[Steph9]

isn't the annulus formula in the formula sheet?

 

[CM_Tutor]

Annulus is the area between two concentric circles. Area = pi * (R² - r²)

Cro_angel is describe an ellipse, where Area = pi * a * b, not an annulus.

The formulae for both these areas are on the formula sheet.

 

[cro_angel]

and thats why u dont ask me maths questions after my maths exam lol.. i dont think straight
thanks cm tutor..
at least i tried but yeh all the circle things are on the formula sheet