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## Probability- hair treatment

tagged by: rolandprowess

This topic has 1 expert reply and 3 member replies
jcnissi Junior | Next Rank: 30 Posts
Joined
12 Jun 2010
Posted:
18 messages
1

#### Probability- hair treatment

Thu Nov 18, 2010 9:55 pm
I'm really good with math but unfortunately, statistics is my weakest point. I'm trying to do all sorts of statistic practice problems so that I can get better. Any help is greatly appreciated!

A particular hair treatment program has caused hair growth in 70% of its users. A random sample of 15 users is obtained. Using the Binomial Probability Distribution, determine the following probabilities:

a) That exactly 14 experienced hair growth.

b) That less than 9 experienced hair growth.

c) That more than 10 experience hair growth.

d) That 15 or more experience hair growth.

e) That 7 or less experienced hair growth.

### GMAT/MBA Expert

Matt@VeritasPrep GMAT Instructor
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Thu Oct 12, 2017 9:18 pm
Not sure how this one got on the front page, but I do this stuff for my day job a lot. Here's an R function I wrote that will answer all five parts:

hairfun <- function(a,b,p,x){sum(sapply(a:b, function(p, x, k){p^k * (1-p)^(x-k) * choose(x, k)}, p=p, x=x))}

where a = the minimum number you want, b = the maximum number you want, p = the probability of each trial, and x = the number of trials, and sapply is found in the dplyr package.

For example, the answer to (2) would be found by running hairfun(0, 8, .7, 15), and the answer to (1) would be hairfun(14, 14, .7, 15).

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goyalsau Legendary Member
Joined
02 Aug 2010
Posted:
866 messages
31
Target GMAT Score:
700+
Fri Nov 26, 2010 11:47 pm
jcnissi wrote:
I'm really good with math but unfortunately, statistics is my weakest point. I'm trying to do all sorts of statistic practice problems so that I can get better. Any help is greatly appreciated!

A particular hair treatment program has caused hair growth in 70% of its users. A random sample of 15 users is obtained. Using the Binomial Probability Distribution, determine the following probabilities:

a) That exactly 14 experienced hair growth.

b) That less than 9 experienced hair growth.

c) That more than 10 experience hair growth.

d) That 15 or more experience hair growth.

e) That 7 or less experienced hair growth.
This is no way a Gmat question..............................

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karanrulz4ever Master | Next Rank: 500 Posts
Joined
25 Jun 2010
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Fri Nov 26, 2010 10:15 pm
You do not have binomial probability questions in GMAT. If you are aiming for GMAT seriously, solve questions which have good chance of appearing on the GMAT test. Don't solve questions which have no chance of appearing.

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Fri Nov 26, 2010 10:43 pm
karanrulz4ever wrote:
You do not have binomial probability questions in GMAT. If you are aiming for GMAT seriously, solve questions which have good chance of appearing on the GMAT test. Don't solve questions which have no chance of appearing.
I agree with Karan, knowing how to solve the chay square stats or f-parameter will not help too much on GMAT.

Once, I tried to solve a work problem with three variables and two equations here; it took me a while. I even had to grab some dusty complex math staff of my sophomore uni year. Trying hard to apply matrix and Gauss solutions, I ended up with parameters for the third variable. Don't waste your time on rocket science what fingers can find.

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