GMAT Probability, Permutations, and Combinations Trick

In this video Magoosh's test prep expert, Erika, shares a useful trick for solving probability, permutation, and combination questions on the GMAT math section!

00:00 - Erika introduces the video
01:00 - What to solve for
01:54 - Probability Example
07:00 - Permutations and Combinations

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[ishikabansal]

Erika is a great teacher! Kudos to Magoosh for getting her on board. 😀

[jaskeeratsingh]

Hi. Great video as always.
The equilateral traingles can be found easily.
Draw a circle. Mark 15 equidistant dots on it (as given in the question). To draw an equilateral triangle with 1st dot selected, select 5th and 10th dot. For equilateral triangle with 2nd dot, select 6th and 11th dot and so on which gives 5 equilateral triangles.

[ArathiNayak]

How the last question was solved blew my mind!

[ivandobrev]

You are awesome! Thanks to the whole Magoosh team!

[soumyadeepdas]

THANKS ERIKA YOU ARE AN AWESOME TEACHER!! ALL THE ADVICES AND ANECDOTES WHERE REALLY USEFUL!!

[nehalvarma]

Thank you so much to Erika and the Magoosh team

[mbaman]

my favourite teacher <3 looking forward to more lectures from erika mam

[jaipurian_vegan]

one doubt ma'am, on the "atleast" prob question, the six sided, why haven't you consider taking 6 as one of the possibility (1, 2, 4, 6)?

[sinjanmajumder]

Wow ! This is a classic one. Loved it !

[MariaYeko-dvxn]

Total combinations of triangles = 15C3 = 455 But to get equidistant dots = 15/3 = 5 different set of dots that form equilateral triangle. Now subtract to get 455-5 = 450

[sudhansusingh]

Thank you for the video. Gained good knowledge

[kartikdixit]

Thanks Erika... Was really helpful.. looking forward to some more videos.

[shanicesegolenemaatchideku]

Sorry bit you got me lost at 11:19. I don't understand how you did the divisions of the factorial.

[learningdesignstudios]

Hi Erika/Magoosh, pardon me but I'm not able to find the blog article which explains the last problem (circle/triangles). Can you please share the link?

[juancarloscevallos]

After seeing all of your GREAT explanations (thx 4 that), I only have one question, and I'm afraid is kind of a dumb one (lol). Last problem, the one with the equilateral triangles... The 15 factorial (15!) was 15 x 14 x 13. My question is: Doesn't the factorial (!) mean 15 x 14 x 13 x 12 x 11 x 10 and so on til 1? I mean, how do you know that you needed to stop at 13? Thanks

[vishalrao]

Hello, Erika Is a specialised tutoring plan available for GMAT currently I already have a strong base in quants and need to advance it and have medium verbal ability. Planning for gmat in 4 months !!

[EEBAsrithaDevineni]

hi erika!
where can i find your teaching for gmat in magoosh.

[collinsondiek]

If you simplify 2/6 in the first question , it becomes 1/3
raised to power 4 it becomes 1/81

1-(1/81) = 80/81 which E. can you explain why you simplify in the 2nd question and not in the 1st question

[malavthakor]

For question no 2. Why could we not just choose (1/3)^8??

[heemoyemeni]

You said the write answer is 80 why you change it to 77 how we can know that