Assuming that the chance of a traffic accident in a day in a street of Delhi is 0.001.

On how many days, out of a total of 500 days can we expect (I) no accident (ii) more than 3 accidents, if there are 1000

such streets in the whole city. ( use 1/e = 0.3679)??

It is question of poisson's distribution.
Let x be the number of streets in which accident occurs be the poisson variable.
By poisson's distributions
P(x=r) =e-mmrr!, r = 0,1,2..Here n =1000, p =0.001 therefore m =np =1000×.001=1Hence P(x=r) =e-1(1)rr!=e-1r!, r = 0,1,2..1000(1) P(accident in no street)=P(x=0) =e-10!=0.36791=0.3679Hence no of days expecting accident in no street =N×P(x=0) = 500×0.3679 =184 Days(approx)(2)P(Accident in more than three street)=P(x>3)=1-P(x3)=1-[P(x=0)+P(x=1)+P(x=2)+P(x=3)]=1-[e-10!+e-11!+e-12!+e-13!]=1-0.3679[83]=0.0189Hence no.of days expecting accident in more than three streets =N×P(x>3) =500×0.0189 =9days(approx)   

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