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Question Number 199310 by necx122 last updated on 01/Nov/23

What is the probability that in a class   of 18 people, there exists a group of 3  people born on the same day of the  week?

Whatistheprobabilitythatinaclassof18people,thereexistsagroupof3peoplebornonthesamedayoftheweek?

Commented by deleteduser1 last updated on 01/Nov/23

1

1

Answered by deleteduser1 last updated on 01/Nov/23

There are only 7 days in a week,and the number  of people has exceeded twice that amount,  there must be a group of three people with the  same day.

Thereareonly7daysinaweek,andthenumberofpeoplehasexceededtwicethatamount,theremustbeagroupofthreepeoplewiththesameday.

Commented by mr W last updated on 01/Nov/23

in following example there is no  group of three people on the same day:  1 person on monday  1 person on tuesday  2 people on wednesday  2 people on thursday  5 people on friday  7 people on saturday  no people on sunday

infollowingexamplethereisnogroupofthreepeopleonthesameday:1persononmonday1personontuesday2peopleonwednesday2peopleonthursday5peopleonfriday7peopleonsaturdaynopeopleonsunday

Commented by deleteduser1 last updated on 01/Nov/23

We can pick a group of 3 from the 5 or 7 on   Friday or Saturday respectively

Wecanpickagroupof3fromthe5or7onFridayorSaturdayrespectively

Commented by deleteduser1 last updated on 01/Nov/23

The question didn′t state “of ′only′ 3 people”  or a day with 3 people only.

Thequestiondidntstateofonly3peopleoradaywith3peopleonly.

Commented by necx122 last updated on 01/Nov/23

unfortunately, I dont know the exact answer as my son just brought it to me. It's quite tricky but I think I can understand from the analysis from the solvings. Thank you sirs.

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