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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: cama23 on August 26, 2010, 09:34:50 pm

Title: question on finding n in binomial probability distribution
Post by: cama23 on August 26, 2010, 09:34:50 pm: if anyone could help me with this one would be greatly appreciated!
Rex is shooting at a target. His probability of hitting the target is .6. What is the number of shots needed for the probability of Rex hitting the target exactly five times to be more than 25%
Title: Re: question on finding n in binomial probability distribution
Post by: 98.40_for_sure on August 26, 2010, 09:44:28 pm: nCr(n,5) x (0.6)^5 x (1-0.6)^(n-5) > 0.25
Title: Re: question on finding n in binomial probability distribution
Post by: cama23 on August 26, 2010, 09:48:06 pm: yeah did that on the calc and set it equal to .35 and it spat out a lot of mumbo jumbo haha
Title: Re: question on finding n in binomial probability distribution
Post by: stonecold on August 26, 2010, 09:50:04 pm: If you're on a ClassPad, you're screwed. On a TI, change the inequality into an equals sign and it should be smooth sailing.
Title: Re: question on finding n in binomial probability distribution
Post by: cama23 on August 26, 2010, 09:51:41 pm: im on a classpad 330, so i guess im screwed!
Title: Re: question on finding n in binomial probability distribution
Post by: vea on August 27, 2010, 08:46:34 pm: What classpad are you using?

I'm using Classpad 330 3.003 and it's all good for me.
Title: Re: question on finding n in binomial probability distribution
Post by: happyhappyland on August 27, 2010, 09:19:49 pm: Quote from: stonecold on August 26, 2010, 09:50:04 pm
If you're on a ClassPad, you're screwed. On a TI, change the inequality into an equals sign and it should be smooth sailing.

Same for classpad just change it to equals and works fine.
Title: Re: question on finding n in binomial probability distribution
Post by: cama23 on August 27, 2010, 10:22:14 pm: im on a classpad 330, tryed it using the equals and didnt work for me!
Title: Re: question on finding n in binomial probability distribution
Post by: happyhappyland on August 28, 2010, 08:50:19 pm: Quote from: cama23 on August 27, 2010, 10:22:14 pm
im on a classpad 330, tryed it using the equals and didnt work for me!

It is the latest version?
Title: Re: question on finding n in binomial probability distribution
Post by: Stroodle on August 31, 2010, 05:16:55 pm: I've got the latest classpad update and it doesn't seem to work in the main section. e.g. can't work out how to solve $\binom{x}{5}(0.6)^5(0.4)^{x-5}>0.25$ for $x$ .
You can do it in the statistics section, but it's a bit of a pain in the butt...
Title: Re: question on finding n in binomial probability distribution
Post by: stonecold on August 31, 2010, 05:19:30 pm: how'd you do it so I can tell my friends if you don't mind...they all have classpads.
Title: Re: question on finding n in binomial probability distribution
Post by: Mao on August 31, 2010, 06:12:00 pm: Do it by trial and error. If you want $\binom{x}{5}(0.6)^5(0.4)^{x-5}>0.25$

Substitute in a number say, x=3, and keep playing 'the price is right' until you have met the condition.
Title: Re: question on finding n in binomial probability distribution
Post by: Andiio on September 11, 2010, 12:56:26 am: You have to find the log e of both once you define the equation with the inequality sign
Title: Re: question on finding n in binomial probability distribution
Post by: LFTM on September 12, 2010, 02:36:47 pm: Hey guys i know how to do this on the classpad, but make sure it is updated to the latest version.

You go to Spreadsheet and you type in 1 in A1. Now go to EDIT, FILL RANGE. For the formula you type in =A1+1 (make sure to put the equal sign). For the range type in A2:A100 and then press OK. Now go to CALC, DISTRIBUTION, select BINOMIAL PD. x=5, number of trials type in A1 and the prob. of success is 0.6. Then go to next, output and make sure the results is in B1 and paste. Now tap on B1(should have zero in it) then go to EDIT, FILL RANGE, the formala should already be there, just set the range as B1:B100 and press OK.

When you look down column B you can see Rex needs 7 shots for the prob. to be more than 25%.

Hope this isn't confusing. Make sure when you're typing the letters in you use the ones at the top of the screen and not the variables.

Theres another way of solving problems like these, if i remember i'll post it up.