Question

ong Kong’s Mai Po marsh is an important migratory stopover for more than 100,000 birds per year from Siberia to Australia. Many of the bird species that stop in the marsh are endangered, and there are no other suitable wetlands to replace Mai Po. Currently the Chinese government is considering building a large housing project at the marsh’s boundary, which could adversely affect the birds. Environmentalists estimate that if the project goes through, there will be a 60% chance that the black-faced spoonbill (current world population = 450) will not survive. It is estimated that there is a 70% chance the Chinese government will go ahead with the building project. What is the probability of the species’ survival (assuming no danger if the project doesn’t go through)?

Answer 1

Let P =Probability

S =Survives

S^c =Does not survive

G =Government goes ahead with the project

G^c =Government does not go ahead with the project

Given:

P(G) =70% =0.7

P(G^c) =1 - 0.7=0.3

P(S^c/G) =60% =0.6

P(S/G) =1 - 0.6 =0.4

No danger if the project doesn’t go through. So, P(S/G^c) =100% =1

P(S^c/G^c) =1 - 1 =0

Tree diagram:

Now,

The probability of the species’ survival =P(S) =P(SG) + P(SG^c) =0.28 + 0.3 =0.58 =58%