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Question Number 76774 by benjo 1/2 santuyy last updated on 30/Dec/19

The probability that the birth days of  six different persons will fall in exactly  two calendar months is

Theprobabilitythatthebirthdaysofsixdifferentpersonswillfallinexactlytwocalendarmonthsis

Commented by mr W last updated on 30/Dec/19

((11)/(7776)) ?

117776?

Commented by benjo 1/2 santuyy last updated on 30/Dec/19

i′m got 341/12^5  sir

imgot341/125sir

Commented by benjo 1/2 santuyy last updated on 30/Dec/19

may be i′m wrong

maybeimwrong

Commented by benjo 1/2 santuyy last updated on 30/Dec/19

how your get it sir ?

howyourgetitsir?

Commented by mr W last updated on 31/Dec/19

probability their birthdays are in  the same month: C_1 ^(12) ×((1/(12)))^6 =(1/(248321))  the same 2 monthes: C_2 ^(12) ×((2/(12)))^6 =((11)/(7776))  the same 3 monthes: C_3 ^(12) ×((3/(12)))^6 =((55)/(1024))  the same 4 monthes: C_4 ^(12) ×((4/(12)))^6 =((55)/(81))  ......  the same 12 monthes: C_(12) ^(12) ×(((12)/(12)))^6 =1

probabilitytheirbirthdaysareinthesamemonth:C112×(112)6=1248321thesame2monthes:C212×(212)6=117776thesame3monthes:C312×(312)6=551024thesame4monthes:C412×(412)6=5581......thesame12monthes:C1212×(1212)6=1

Commented by mr W last updated on 31/Dec/19

to choose two monthes from 12  there are C_2 ^(12)  possibilities.    let′s take monthes January and  February. for one person the  probability that his birthday is in   Jan. or Feb. is (2/(12))=(1/6).  for six persons the probability  that their birthdays are in Jan. or  Feb. is then ((1/2))^6 .  for any two monthes:  ⇒p=C_2 ^(12) ×((1/6))^6 =((11)/(7776))

tochoosetwomonthesfrom12thereareC212possibilities.letstakemonthesJanuaryandFebruary.foronepersontheprobabilitythathisbirthdayisinJan.orFeb.is212=16.forsixpersonstheprobabilitythattheirbirthdaysareinJan.orFeb.isthen(12)6.foranytwomonthes:p=C212×(16)6=117776

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