Question

Vaishnave was walking to a hill,in the mid way she came across several people,(girl,boy, small baby,old citizens)

If the probability of coming across a Small baby is twice the probability of seeing a old citizen which is half of probability of either girl or boy
.

If she came across atleast 1000 people, explain how many were small babies,old citizens, either girls or boys

And probability of seeing either girl or boy is 2/5

Answer 1

Hi pratiksha 
  probability appearing of a boy or girl =2/5
and probability of appearing of appearing an old citizen = 1/5
probability of appearing a small baby =  2/5
ATQ 
2/5=x/1000
x=2/5X1000
x=400
no. of girl or boy= 400 
no of old peoples = 200
no . of small babies =400
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Answer 2

She came across :  'a' number of girls,  'b' number of boys, 'c' number of  small babies, and  'd' number of  old citizens.

P(a small baby) = 2 * P(an old citizen)
P(a girl or a boy)  = 2 * P(an old citizen)
ie., P(a girl) + P(a boy) = 2 * P(an old citizen)
Given   2/5 = 2 * P(an old citizen)
  =>  P(an old citizen) = 1/5
   =>  P(a small baby) = 2/5

Total number of persons = N = 1000 or more
   Number of small babies = 2/5 * N = 400 or more
   Number of old citizens = 1/5 * N = 200 or more
   Number of girls and boys  total = remaining = 400 or more