GMAT Probability, Permutations, and Combinations Trick

[@ishikabansal9031]

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

[@MagooshGMAT]

We are lucky to have such great instructors!

[@jonashill2420]

seriously! if she's not in it i don't watch 😂

[@jaskeeratsingh5491]

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.

[@MrIndman]

1, 1+5, 1+10; 2, 2+5, 2+10;....

[@ArathiNayak]

How the last question was solved blew my mind!

[@MagooshGMAT]

Sometimes these tough problems aren't as tough as they seem!

[@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)?

[@soumyadeepdas1536]

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

[@nehalvarma8576]

Thank you so much to Erika and the Magoosh team

[@MagooshGMAT]

Our pleasure, thanks for stopping by! 😁

[@ivandobrev122]

You are awesome! Thanks to the whole Magoosh team!

[@MariaYeko-dv5xn]

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

[@mbaman7363]

my favourite teacher

[@MagooshGMAT]

Woohoo! Thanks for sharing :)

[@derisazahara7696]

Great video!

[@abheetnigam]

Erikaaaa is backk!!!!

[@juancarloscevallos3899]

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

[@Marshmellow3971]

When you take a combination of xCy, you’re dividing X!/Y!(X-Y)! In this case 15!/3!(12!), you can express 15! As 15x14x13x12… and 12! As 12x11x10… when you divide 15!/12! Everything after 13 cancels out, because it is also part of 12!.

[@collinsondiek9943]

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

[@therandomthings9128]

You solved wrong.

[@gianleking]

So useful omg

[@sinjanmajumder3316]

Wow ! This is a classic one. Loved it !

[@MagooshGMAT]

Glad you liked it! Thanks for the comment :)

[@kartikdixit8100]

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

[@MagooshGMAT]

Awesome, we're glad you liked it! Thanks for commenting :)

[@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?

[@MagooshGMAT]

Hello there! Here's the one you're looking for :) magoosh.com/gmat/difficult-gmat-counting-problems/

[@learningdesignstudios]

@@MagooshGMAT Thank you team!

[@sudhansusingh2886]

Thank you for the video. Gained good knowledge

[@MagooshGMAT]

Thanks for the comment, we're glad it was useful for you! :)

[@learningbud1209]

A very nice explanation. Thank you 🙏

[@MagooshGMAT]

Woohoo! Glad you liked it :) Thanks for stopping by!

[@vishalrao5107]

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 !!

[@MagooshGMAT]

Not at Magoosh right now, but there are services elsewhere. Good luck!

[@cameronlarson4046]

Thanks! This helped.

[@AJ-et3vf]

Great video! Thank you!

[@MagooshGMAT]

You are welcome!🙌

[@andresjustinianod.7067]

Thanks Erika!

[@vinayviking]

What happened to Prepscholar GMAT?

[@malavthakor2202]

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

[@therandomthings9128]

Because they specifically asked for AT LEAST 1 blue marble.

[@EEBAsrithaDevineni]

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

[@shanicesegolenemaatchideku770]

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

[@MagooshGMAT]

You can review how to divide factorials here: gmatclub.com/blog/2012/01/gmat-permutations-factorial-trick/

[@yashchavan9403]

Great Tips 👍

[@nileshmishra4602]

Awesome video

[@MagooshGMAT]

Thank you!🙌

[@kartikization]

I solved all 😅

[@MagooshGMAT]

Great job!

[@ashishsinha9035]

Great!

[@MagooshGMAT]

Thank you!

[@heemoyemeni2220]

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

[@MagooshGMAT]

Even though the total number of possible combinations is 80, there is a restriction in the question: "the paper, ribbon, and bow cannot all be the same color." So that reduces the number of combintions.

[@user-dv2jw8my1r]

Ok

[@MagooshGMAT]

👌

[@heemoyemeni2220]

I have an exam after one week can you help me please is there any one here can help me ?

[@MagooshGMAT]

We'd recommend checking out other videos for practice and focusing your studies on the areas your struggling with the most. Good luck!

[@MariaYeko-dv5xn]

That last questions didn't understand completely