Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store
seo-qna
SearchIcon
banner

There are 20 seats in some rows of a movie theatre and 5 people sit randomly in this row. The probability that no two persons sit side by side, is
(a) 91323(b) 232323(c) 120323(d) none of these

Answer
VerifiedVerified
531.3k+ views
like imagedislike image
Hint: In this question first find the total possible outcomes by making 5 people sit in 20 seats of a row. Then the favorable number of outcomes are computed by considering the group of 5 people as 1 subtracted by the total possible cases.

Complete Step-by-Step solution:
Total number of seats in a row is 20.
Total number of persons is 5.
Now the number of ways to arrange 5 persons on 20 seats is 20P5.
Now consider 5 persons as 1 so the total number of seats become (20 – 5 + 1) = 16
So the number of ways to arrange 1 person (which is equal to 5) on 16 seats is16P5.
So the number of ways so that two persons sit side by side is =16P5.
So the number of ways so that two persons sit side by side is = 20P516P5
Now as we know that the probability (P) is the ratio of favorable number of outcomes to total number of outcomes that is P = Favorable outcomeTotal number of outcome
P=20P516P520P5
Now as we know that nPr=n!(nr)! so use this property in above equation we have,
P=20!(205)!16!(165)!20!(205)!
Now simplify this we have,
P=20!15!16!11!20!15!=116!×15!20!×11!
P=16!×15!20!×11!=116!×15×14×13×12×11!20×19×18×17×16!×11!=115×14×13×1220×19×18×17=191323P=232323
So this is the required answer.
Hence option (B) is correct.

Note: The concept behind taking group of 5 people into one was to find the probability of no two of them sitting together, thus instead of finding it directly we have found it conversely, if we make them sit together and then subtract from the total possible arrangements than it gives the arrangements of them no being seated together. This concept helps solve problems of this kind.
Latest Vedantu courses for you
Grade 10 | CBSE | SCHOOL | English
Vedantu 10 CBSE Pro Course - (2025-26)
calendar iconAcademic year 2025-26
language iconENGLISH
book iconUnlimited access till final school exam
tick
School Full course for CBSE students
PhysicsPhysics
Social scienceSocial science
ChemistryChemistry
MathsMaths
BiologyBiology
EnglishEnglish
₹41,000 (9% Off)
₹37,300 per year
Select and buy