Question

a)Five measurements have been taken from a population having mean 42 and variance 16. The probability that the average of these measurements exceeds 42.7 is

Group of answer choices

not to be determined from the given information, without additional assumptions.

0.244

0.126

0.366

0.411

b)LC50 for a chemical is the lethal concentration for 50% of animals or humans. For example, if the water contains a chemical at the LC50 concentration, 50% of the fish population in the water would die. Environment Canada collects data on LC50 concentrations. A 95 % confidence interval for the true mean LC50 with a random sample of 181 measurements is (15.8, 18.4). What is the standard error of the mean?

Group of answer choices

1.3

14

2.6

5.035

.66

Answer 1

a) not to be determined from the given information, without additional assumptions.

b)

confidence interval is                  
lower limit =    15.8              
upper limit=   18.4              

margin of error = (upper limit-lower limit)/2= (   18.4   -   15.8   ) / 2 =   1.3
                  
margin of error ,E = Z*std error

Level of Significance ,    α =    0.05
'   '   '
z value=   z α/2=   1.960

std error = E/Z = 1.3 / 1.96 = 0.66 (answer)