Answer:
a. B/C Ratio = 0.296  
b. B/C Ratio = 2.964 
c. Y = 12.05 USD will be the maximum amount charged by the manager. 
    Y = 12.05 x 10 = 120.54 USD for the whole group of 10
Explanation:
Solution: 
Data Given: 
Number of Individuals = 10 
Number of Stones = 100
Life Expectancy = 10 Years 
Annual benefit = 8.25 USD 
Stone Removal Cost = 2.50 USD
Interest Rate = 2% 
a. If all the stones are removed by one individual: 
Cost = 100 stones x Stone Removal Cost 
Cost = 100 x 2.50 = 250 USD 
Now, we have to calculate the Benefit/Cost Ratio for this individual by using the following formula: 
B/C Ratio =  
 
Where, 
AB = Annual Benefit = 8.25 USD 
(P/A, 2%, 10) = 8.983      (From the compound interest table) 
Cost = 250 USD 
B/C Ratio =  
 
B/C Ratio = 0.296 
b. Each individual removing 10 stones. 
Number of individuals = 10 
So, the cost of removing the stones will be: 
Cost = 10 x 2.50 = 25 USD 
So, 
B/C Ratio =  
  
B/C Ratio =  
 
  B/C Ratio = 2.964
c. 
In this part, we are already given the B/C ratio, now we need to calculate the maximum amount charged by the manager for the help. 
B/C ratio = 2 
Let, Y be the amount of the manager. So, 
B/C Ratio =   
   
Plugging in the values and solving for Y: 
2 =  
 
50 + 2Y = 8.25 x 8.983 
2Y = 74.109 - 50 
2Y = 24.109  
Y = 24.109/2
Y = 12.05 USD will be the maximum amount charged by the manager. 
Y = 12.05 x 10 = 120.54 USD for the whole group of 10