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# A certain store sells small, medium, and large toy trucks i

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Director
Joined: 29 Nov 2012
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A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Jan 2013, 05:36
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A certain store sells small, medium, and large toy trucks in each of the colors red, blue, green, and yellow. The store has an equal number of trucks of each possible color-size combination. If Paul wants a medium, red truck and his mother will randomly select one the trucks in the store, what is the probability that the truck she selects will have at least one of the two features Paul wants?

A. 1/4
B. 1/3
C. 1/2
D. 7/12
E. 2/3
[Reveal] Spoiler: OA

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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Jan 2013, 06:04
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fozzzy wrote:
A certain store sells small, medium, and large toy trucks in each of the colors red, blue green, and yellow. The store has an equal number of trucks of each possible color-size combination. If Paul wants a medium, red truck and his mother will randomly select one the trucks in the store, what is the probability that the truck she selects will have at least one of the two features Paul wants?

A. 1/4
B. 1/3
C. 1/2
D 7/12
E. 2/3

let there be x number of trucks of all possible color-size combination.
probability that the truck she selects will have at least one of the two features Paul wants can be found by subtracting the probability of selecting a truck that doesn't has either of the property i.e. it is neither red in color nor of medim size from 1.

In the diagram attached, the I crossed off all the desired results i.e. cancelled all the possible combination of red-medium.
# of remaining outcomes= # of blue circles = # of trucks that don't have either of the desired property.

No. of colors=4
no. of sizes=3
Total outcomes=12

Remaining outcomes=6
hence probability that truck is neither red nor of medium size is $$6/12$$.
hence probability that the truck she selects will have at least one of the two features Paul wants will be $$1 - 6/12$$ or $$1/2$$
+1C
Attachments

probability.png [ 9.42 KiB | Viewed 12465 times ]

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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Jan 2013, 07:53
Great Explanation! Thanks!
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Jan 2013, 09:05
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Assume there are 1 of each giving - 3 sizes x 4 colours = 12 trucks

Since the q is asking for "at least one" (medium truck or red truck) let's calculate probability of selecting neither a red or medium truck and subtract from 1

Therefore - 1 - 6/12 = 1/2
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Jan 2013, 09:22
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The key is to take in account whenever see you the word $$AT$$ $$Least$$ is to subtract the other probability from 1

In this case you DO NO want the large and the small size so $$2/3$$$$AND$$ (means $$*$$) the other colors so$$3/4$$

From this $$1 - 2/3 * 3/4 = 1 - 6/12 = 6/12 = 1/2$$
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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27 Jan 2013, 05:24
fozzzy wrote:
A certain store sells small, medium, and large toy trucks in each of the colors red, blue green, and yellow. The store has an equal number of trucks of each possible color-size combination. If Paul wants a medium, red truck and his mother will randomly select one the trucks in the store, what is the probability that the truck she selects will have at least one of the two features Paul wants?

A. 1/4
B. 1/3
C. 1/2
D 7/12
E. 2/3

Please add a comma between blue and green. I mistook it as 1 category!
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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08 Oct 2014, 17:05
I went with 1/2. I think the simplest way is to calculate 1 - P (0 features being chosen).
P (0 features) = 2/3 (the other two sizes) times 3/4 (the other two colors) = 1/2
1-1/2 = 1/2
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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09 Oct 2014, 12:56
carcass wrote:
The key is to take in account whenever see you the word $$AT$$ $$Least$$ is to subtract the other probability from 1

In this case you DO NO want the large and the small size so $$2/3$$$$AND$$ (means $$*$$) the other colors so$$3/4$$

From this $$1 - 2/3 * 3/4 = 1 - 6/12 = 6/12 = 1/2$$

I understand this reasoning and it makes perfect sense. But why in this case it doesn't work the probability of each:

1/3+1/4 = 7/12 ??

Thanks!
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Joined: 02 Sep 2009
Posts: 44655
Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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10 Oct 2014, 02:33
nachobioteck wrote:
carcass wrote:
The key is to take in account whenever see you the word $$AT$$ $$Least$$ is to subtract the other probability from 1

In this case you DO NO want the large and the small size so $$2/3$$$$AND$$ (means $$*$$) the other colors so$$3/4$$

From this $$1 - 2/3 * 3/4 = 1 - 6/12 = 6/12 = 1/2$$

I understand this reasoning and it makes perfect sense. But why in this case it doesn't work the probability of each:

1/3+1/4 = 7/12 ??

Thanks!

You should subtract the overlap: 1/3*1/4 = 1/12 from 7/12.
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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10 Oct 2014, 08:31
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let me explain in easy terms

the question asks atleast of the two(red-medium).So we gonna find trucks which dont have any of the mentioned or asked charateristic.i.e neither medium nor red and later subtract it.

first,total outcomes-4C1(for any colored truck)*3C1(size of the truck)=12
second,(truck neither medium nor red)=SB,SG,SY LB,LG,LY
so the required probality then toy selkected is medium-red or any of the two=1-(6/12)=1/2

other Solution=

either red or medium or both=MR,MB,MG,MY RS,RM,RL( HERE WE HAVE COUNTED MR or RM twice,so take only one)

prob=6/12=1/2

C.

hope it helps

-h
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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31 Mar 2015, 09:01
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We have P(M or R) = P(M) + P(R) - P(M)*P(R) = 1/3 + 1/4 - 1/3*1/4 = 7/12 - 1/12 = 1/2.
M: Medium
R: Red
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Re: A certain store sells small, medium, and large toy trucks i [#permalink]

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31 Mar 2015, 11:00
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fozzzy wrote:
A certain store sells small, medium, and large toy trucks in each of the colors red, blue, green, and yellow. The store has an equal number of trucks of each possible color-size combination. If Paul wants a medium, red truck and his mother will randomly select one the trucks in the store, what is the probability that the truck she selects will have at least one of the two features Paul wants?

A. 1/4
B. 1/3
C. 1/2
D. 7/12
E. 2/3

Probability of NOT selecting medium out of 3 sizes = 2/3
Probability of NOT selecting red out of 4 colours = 3/4

Total probability of NOT selecting red and medium = (2/3)*(3/4) = 1/2

Required probability = 1 - 1/2 (this will select at least one of red and medium)
= 1/2
Hence option (C).

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Optimus Prep's GMAT On Demand course for only $299 covers all verbal and quant. concepts in detail. Visit the following link to get your 7 days free trial account: http://www.optimus-prep.com/gmat-on-demand-course Intern Status: Preparing for GMAT Joined: 14 Jun 2011 Posts: 26 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 18 Sep 2015, 16:53 can someone please explain why below approach is wrong. assume there is one truck of each combo Small 4 trucks ( 1 Red, 1 Blue, 1 Green, 1 yellow) Medium 4 trucks ( 1 Red, 1 Blue, 1 Green, 1 yellow) Large 4 trucks ( 1 Red, 1 Blue, 1 Green, 1 yellow) Now, probability of choosing red truck is 3/12 = 1/4 probability of choosing medium truck is 4/12 = 1/3 probablity of either red or medium is 1/4 + 1/3 ( which is same as atleast red or medium) = 7/12 This is obviously wrong answer but i cant figure where is the problem. _________________ Its not over yet!!! Intern Joined: 15 Apr 2015 Posts: 13 Location: India Schools: EDHEC (A) GMAT 1: 620 Q44 V31 GPA: 3.25 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 05 Apr 2016, 12:40 Bunuel wrote: nachobioteck wrote: carcass wrote: The key is to take in account whenever see you the word $$AT$$ $$Least$$ is to subtract the other probability from 1 In this case you DO NO want the large and the small size so $$2/3$$$$AND$$ (means $$*$$) the other colors so$$3/4$$ From this $$1 - 2/3 * 3/4 = 1 - 6/12 = 6/12 = 1/2$$ I understand this reasoning and it makes perfect sense. But why in this case it doesn't work the probability of each: 1/3+1/4 = 7/12 ?? Thanks! You should subtract the overlap: 1/3*1/4 = 1/12 from 7/12. Hi Bunuel , can you show this by applyig P and C formula. i tried the non event method, 1-3c2*4c3/3c1*4c1.This is coming out to be 0.There is some issue with the cases in the numerator of the fraction. Intern Joined: 18 Oct 2016 Posts: 3 A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 06 May 2017, 03:24 1 This post received KUDOS There are 3 sizes of trucks in 4 colours each, so a total of 3x4=12 trucks P(M u R) = P(M) + P(R) - P(M n R) => 4/12 + 3/12 - 1/12 => 6/12 => 1/2 (Answer C) Director Joined: 17 Dec 2012 Posts: 635 Location: India Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 31 May 2017, 03:35 fozzzy wrote: A certain store sells small, medium, and large toy trucks in each of the colors red, blue, green, and yellow. The store has an equal number of trucks of each possible color-size combination. If Paul wants a medium, red truck and his mother will randomly select one the trucks in the store, what is the probability that the truck she selects will have at least one of the two features Paul wants? A. 1/4 B. 1/3 C. 1/2 D. 7/12 E. 2/3 1. Favorable outcome is that, the truck should be medium or red or both 2. The opposite of this is easier to find which is neither medium nor red 3. Number of ways of selecting (large or small) and (blue , green or yellow) is 2*3=6 4. Total number of ways of selecting=3*4=12 5. Probability for opposite of favorable cases is 6/12=1/2 6. Probability for favorable case is 1-(1/2) = 1/2 _________________ Srinivasan Vaidyaraman Sravna http://www.sravnatestprep.com/best-online-gre-preparation.php Improve Intuition and Your Score Systematic Approaches Intern Joined: 15 Aug 2017 Posts: 12 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 01 Jan 2018, 06:25 Bunuel wrote: nachobioteck wrote: carcass wrote: The key is to take in account whenever see you the word $$AT$$ $$Least$$ is to subtract the other probability from 1 In this case you DO NO want the large and the small size so $$2/3$$$$AND$$ (means $$*$$) the other colors so$$3/4$$ From this $$1 - 2/3 * 3/4 = 1 - 6/12 = 6/12 = 1/2$$ I understand this reasoning and it makes perfect sense. But why in this case it doesn't work the probability of each: 1/3+1/4 = 7/12 ?? Thanks! You should subtract the overlap: 1/3*1/4 = 1/12 from 7/12. hi Bunuel , why should we subtract the overlap? since it says at least 1 of the features.shouldnt' it includes red, truck and red + truck? Math Expert Joined: 02 Aug 2009 Posts: 5777 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 01 Jan 2018, 07:43 1 This post received KUDOS Expert's post jtankx90 wrote: Bunuel wrote: nachobioteck wrote: I understand this reasoning and it makes perfect sense. But why in this case it doesn't work the probability of each: 1/3+1/4 = 7/12 ?? Thanks! You should subtract the overlap: 1/3*1/4 = 1/12 from 7/12. hi Bunuel , why should we subtract the overlap? since it says at least 1 of the features.shouldnt' it includes red, truck and red + truck? hi... overlap is added twice, ones with red and once with truck, so you have to subtract it once.. _________________ Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html GMAT online Tutor Intern Joined: 15 Aug 2017 Posts: 12 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 01 Jan 2018, 08:08 You should subtract the overlap: 1/3*1/4 = 1/12 from 7/12.[/quote] hi Bunuel , why should we subtract the overlap? since it says at least 1 of the features.shouldnt' it includes red, truck and red + truck?[/quote] hi... overlap is added twice, ones with red and once with truck, so you have to subtract it once..[/quote] ah totally missed that out... thanks! EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 11518 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Re: A certain store sells small, medium, and large toy trucks i [#permalink] ### Show Tags 10 Mar 2018, 12:09 Hi All, This question can be solved with a real simple "brute force" approach. There are 3 types of toy trucks (small, medium and large) and 4 colors (red, blue, green and yellow). We're told that there are equal numbers of each color-size combination and we're asked what the probability is of randomly pulling a truck that is RED or MEDIUM or BOTH. I'm going to list out all of the possibilities and put a * next to the ones that fit what we're looking for: Small Red * Small Blue Small Green Small Yellow Medium Red * Medium Blue * Medium Green * Medium Yellow * Large Red * Large Blue Large Green Large Yellow 6 of the 12 options are red or medium or both. Final Answer: [Reveal] Spoiler: C GMAT assassins aren't born, they're made, Rich _________________ 760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com # Rich Cohen Co-Founder & GMAT Assassin Special Offer: Save$75 + GMAT Club Tests Free
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Re: A certain store sells small, medium, and large toy trucks i   [#permalink] 10 Mar 2018, 12:09
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