Is this right?

[alexjohnson16]

Taking an online quiz for my math class... Does this look right???

Q: On a standardized math exam, the mean is 120, with a standard deviation of 12, find the percentage of people whose scores were less than 132.

My A: 132 is within one deviation of 120, therefore the empirical rule states that 68% of all data values lie within this deviation of the mean.

The 68% lies equally on both sides of the mean, so 34% is above 120. 50% of the scores lie above 120, so we want to subtract 34% from 50% = 16%. We must than add everything under 120, so 50% + 16% = 66%.

66% of scores were under 132.

Is this correct?

 

[Syringer]

You want to add everything below 120, which is 50%, plus the portion that is between 120-132..which isn't 16%.

Hint: 68% got between mean - std dev and mean + std dev.

Draw a normal distribution graph, and plot 120 and 132 on there..it'll help.

 

[alexjohnson16]

Are you sure? 😕

 

[Syringer]

Since I'm procrastinating, here's a pic;

http://tinypic.com/ic8gat.jpg

 

[alexjohnson16]

So the answer is 84%?

The lesson said nothing of these graphs. That makes it a lot easier.

 

[Schadenfreude]

Woah, he finishes the topic for a change!

AND IT'S NOT EVEN HIS THREAD!! :Q:Q:Q

(btw, yep - he's right)

 

[Syringer]

Yup.

Think about it..if 68% lied within one std deviation of the mean, both to the left and right..how can 66% of all the data lie below a point one std dev above the mean?

 

[alexjohnson16]

Gah, that was so simple.

<----assjack.

Thanks for the help, Syringer. 😀 :beer:

 

[sygyzy]

Best homework thread ever.

 

[alexjohnson16]

Originally posted by: sygyzy
Best homework thread ever.

???

 

[Syringer]

Originally posted by: alexjohnson16

Originally posted by: sygyzy
Best homework thread ever.

???

😕

 

[bradruth]

It's 84%.

 

[sygyzy]

What are you guys rolling your eyes at? I was being serious. Someone asked a homework question and presented his answer and why he thought it was right. Another member offered help, and even provided a diagram. And there was no flaming.

Except now you guys are rolling your eyes at me. Way to ruin a great thread.

 

[Syringer]

:roll:




😉

 

[Minjin]

If you have a TI, I think it would be normalcdf(132,120,12).

Mark

 

[Schfifty Five]

Originally posted by: bradruth
It's 84%.

way to chime in after it's been figured out for a few hours already.

 

[bradruth]

Originally posted by: Schfifty Five

Originally posted by: bradruth
It's 84%.

way to chime in after it's been figured out for a few hours already.

Yeah, it's always best to leave one person answering a question, because we know that the first person to answer a question is always right. You wouldn't want someone else to confirm said answer. That would just be foolish. No, just go for the first answer you get. That's really the best way to handle the situation. It really is.

 

[mzkhadir]

Originally posted by: Syringer

Originally posted by: alexjohnson16

Originally posted by: sygyzy
Best homework thread ever.

???

😕

 

[Minjin]

Originally posted by: Minjin
If you have a TI, I think it would be normalcdf(132,120,12).

Mark

Now that I'm home I realize that I forgot to put the left value in the entry above. It should be: normalcdf(left value, right value, mean, standard deviation)

Normalcdf is found by pressing 2nd and then STAT (to access DISTR) on TI-83 and TI-84s. If you don't have one of these, do a google search for Virtual TI. Its a good emulator program.

so: normalcdf(-1e99,132,120,12)
gives you: .8413447

Mark