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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: qshyrn on September 18, 2010, 09:17:14 pm

Title: can someone solve this using CALC?
Post by: qshyrn on September 18, 2010, 09:17:14 pm: this is from the 2009 vcaa
i tried solving this (see image) but my ti-89 fucks up and then i have to take the batteries out and wait 10 minutes.. wouldnt be ttooo great in an exam (does anyone know how to cancel/stop a command) .
Title: Re: can someone solve this using CALC?
Post by: stonecold on September 18, 2010, 09:18:58 pm: I swear to god Mathods CAS is so shit. calculators suck, always fuck up and freeze, take ages to draw graphs, and you have to know extra shit...
Title: Re: can someone solve this using CALC?
Post by: fady_22 on September 18, 2010, 10:13:04 pm: Quote from: qshyrn on September 18, 2010, 09:17:14 pm
this is from the 2009 vcaa
i tried solving this (see image) but my ti-89 fucks up and then i have to take the batteries out and wait 10 minutes.. wouldnt be ttooo great in an exam (does anyone know how to cancel/stop a command) .

Just press the ON button, and then enter.
Title: Re: can someone solve this using CALC?
Post by: InitialDRulz on September 18, 2010, 10:24:19 pm: I just tried using my Ti-Nspire, i get an argument mismatch :S
Title: Re: can someone solve this using CALC?
Post by: qshyrn on September 18, 2010, 11:12:23 pm: Quote from: InitialDRulz on September 18, 2010, 10:24:19 pm
I just tried using my Ti-Nspire, i get an argument mismatch :S
u mustve typed somethign wrong... try typing the SD as 'a' , and solve for it.
Title: Re: can someone solve this using CALC?
Post by: moekamo on September 19, 2010, 04:12:07 am: its easier if you recognise that the equation is for the normal distribution curve with $\mu=67$

The integral also means that $\Pr (65.6 < X < 68.4) = 0.99$

You can then convert this to z values to give: $\Pr \left ( -\frac{1.4}{\sigma} < z < \frac{1.4}{\sigma} \right )=0.99$

solving this with the calculator gives $\frac{1.4}{\sigma} = 2.575829303$ and so $\sigma = 0.5435$ to 4 D.P
Title: Re: can someone solve this using CALC?
Post by: taiga on September 19, 2010, 09:53:29 am: you're doing the question wrong ;)
Title: Re: can someone solve this using CALC?
Post by: kriptik on September 19, 2010, 10:39:52 am: i tried using this online website http://www.wolframalpha.com and it couldn't solve it, it said something about error function
Title: Re: can someone solve this using CALC?
Post by: qshyrn on September 19, 2010, 12:17:46 pm: Quote from: moekamo on September 19, 2010, 04:12:07 am
its easier if you recognise that the equation is for the normal distribution curve with $\mu=67$

The integral also means that $\Pr (65.6 < X < 68.4) = 0.99$

You can then convert this to z values to give: $\Pr \left ( -\frac{1.4}{\sigma} < z < \frac{1.4}{\sigma} \right )=0.99$

solving this with the calculator gives $\frac{1.4}{\sigma} = 2.575829303$ and so $\sigma = 0.5435$ to 4 D.P
yeah, i know im meant to do it this way so was just curious if other way would work
Title: Re: can someone solve this using CALC?
Post by: TyErd on September 19, 2010, 12:24:36 pm: moekamo, how did you find out that the z score equals 2.575829303???

and I also tried on the calculator with that massive equation but i cant do it either...

i've attached the actual question
Title: Re: can someone solve this using CALC?
Post by: Duck on September 19, 2010, 12:34:00 pm: On and clear will stop the calc if it's frozen, learnt this in my last sac.
Title: Re: can someone solve this using CALC?
Post by: qshyrn on September 19, 2010, 01:06:53 pm: Quote from: TyErd on September 19, 2010, 12:24:36 pm
moekamo, how did you find out that the z score equals 2.575829303???

and I also tried on the calculator with that massive equation but i cant do it either...

i've attached the actual question
using INVERSE NORMAL on the calculator. Pr(X<65.6)= 0.005 (by symmetry) then you do invnorm(.005) equate the answer isZ , which is equal to (mean-65.6)/SD solve for SD
Title: Re: can someone solve this using CALC?
Post by: TyErd on September 19, 2010, 01:21:41 pm: question on inverse normal, is mean always 0 and SD = 1 ???
Title: Re: can someone solve this using CALC?
Post by: qshyrn on September 19, 2010, 01:29:01 pm: Quote from: TyErd on September 19, 2010, 01:21:41 pm
question on inverse normal, is mean always 0 and SD = 1 ???
yes
Title: Re: can someone solve this using CALC?
Post by: Blakhitman on September 19, 2010, 02:48:50 pm: Quote from: qshyrn on September 19, 2010, 01:29:01 pm
Quote from: TyErd on September 19, 2010, 01:21:41 pm
question on inverse normal, is mean always 0 and SD = 1 ???
yes

If the scores are converted to their standard form.