Question

Suppose the average lifespan of a lab rat is 3.4 years with a standard deviation of 0.8 years. If we obtain a simple random sample of 64 lab rats, what is the probability that the sample average lifespan is at least 3.65 years?

a) 0.0062 b) 0.9938 c) 0.4052 d) 0.0485 e) 0.9515

Answer 1

Solution :

Given that,

mean = = 3.4

standard deviation = = 0.8

= =3.4

= / n = 0.8 / 64 = 0.1

P( > 3.65) = 1 - P( < 3.65)

= 1 - P[( - ) / < (3.65-3.4) /0.1 ]

= 1 - P(z <2.5 )

Using z table

= 1 - 0.9938

= 0.0062

probability= 0.0062