GRE Permutation Practice Question. Rearranging letters. Hard Question

Video solution to a classic GRE permutation practice question testing the concept of rearranging letters of a word with an interesting constraint thrown in.
Question
In how many rearrangements of the letters of the word SCINTILLATING will no two 'I's appear together?
A. 11C3 * 13!
B. (10!)/(2! * 2! * 2!)
C. 11C3 * 3! * 10!
D. 11C3 * (10! / (2! * 2! * 2!))
E. 11!/(2! * 2! * 2!)
More practice questions in GRE permutation combination and probability @ practice-quest...
ACE the GRE with Wizako's GRE classes @ Chennai. Visit classes.wizako... for batch details.

[@WizakoPrepGRE]

Variant 1: 3 boys and 3 girls such that no two boys stand together: 4C3 * 3! * 3! Variant 2: 4 black and 6 white balls such that no two black balls are placed next to each other: 7C4.

[@ramitamohapoo8071]

Sir,would you mind in clarifying whether this is permutation or combination.i got confused in your symbol "C" and i do think its permuatation since order matters here

[@WizakoPrepGRE]

It certainly is a permutation question. The C symbol is used to select 3 places out of the 11 available places where we can place the Is. Hope it clarifies your query. If you still have doubt in this, please do not hesitate to reply to this comment. Best wishes for your GRE prep.

[@gabiayoub7155]

@@WizakoPrepGREso all the elements are using the permutation formula? Why use “C” letter?

[@Tausifsiddiqui]

@@gabiayoub7155 Since all I’s are the same (there’s no I1 I2 I3, etc) there’s no need to do permutation (rearrangement), only selection (combination). Hence C is used in the first element.

[@Tausifsiddiqui]

Since all I’s are the same (there’s no I1 I2 I3, etc) there’s no need to do permutation (rearrangement), only selection (combination). Hence C is used in the first element.

[@gopimacha4321]

can u please explain 2 questions

[@WizakoPrepGRE]

Hello Gopi! Will shoot videos for those two questions and post the URLs here soon.

[@gopimacha4321]

Tq

[@WizakoPrepGRE]

Hello Gopi. Have shot a video with explanatory answer to those two questions. Watch it at kzbin.info/www/bejne/nYumpIyfm8mMqtE

[@rahulravi4979]

What are the answers to the last 2 questions?

[@WizakoPrepGRE]

Hello Rahul. Which 2 questions? Are you referring to questions in the Wizako's GRE question bank? If it is those 2, will add videos next week and upload them.

[@rahulravi4979]

I was referring to the last 2 questions in this video (7:51). Could you share the answers to them?

[@rahulravi4979]

Thank you btw, great videos!

[@WizakoPrepGRE]

Have shot a video with explanatory answer to those two questions. Watch it at kzbin.info/www/bejne/nYumpIyfm8mMqtE

[@dhruvsardana]

Best Quant tutor!