The lifetime of a certain type of battery has a mean value 20 hours and standard deviation 3 hours. A bulk package of these batteries contains 40 randomly selected batteries. The distribution of average life time i g

The distribution of average life time is approximately normallyl distributed with mean 20 hours and standard deviation of 0.4743 hours

Step-by-step explanation:

The Central Limit Theorem estabilishes that, for a normally distributed random variable X, with mean and standard deviation , the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean and standard deviation .

For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.

In this problem

The distribution of average life time is approximately normallyl distributed with mean 20 hours and standard deviation of 0.4743 hours

it's equivalent, so we can say that its equal.

let's call the denominator x and the numerador is 18 less then denominator, x - 18.

multiply

2.x = 5.(x - 18)

2x = 5x - 90

90 = 5x - 2x

90 = 3x

x = 90/3

x = 30

so:

d. 8

step-by-step explanation:

the given radical expression is:

we can rewrite this as:

we express as square numbers to get;

the exponents will now cancel out to give.

the correct answer is d