The lifetime of a certain resistor in a certain application has a mean of 900 hours and a standard deviation of 30 hours. Four resistors are used in sequence (i. e., one after the other), and the total length of time that the four resistors last is recorded. The resistors are independent of one another. What is the mean length of time in hours that the four resistors last?

The mean of the 4 resistor sample will be equal to the mean of the whole population too.

Step-by-step explanation:

The mean (μₓ) and standard deviation of the sample mean (σₓ) are related to the mean (μ) and standard deviation of the population (σ) through the following relationship

μₓ = μ = 900 hours

σₓ = σ/√n = 30/√4 = 30/2 = 15 hours

the answer is b.

step-by-step explanation:

by the trigonometric ratio tangent, tangent equals opposite divided by adjacent.

therefore, tan(50) equals ac/3

multiply each side by 3 to get: ac=3tan(50)

the answer is b.

45.36 feet per second

step-by-step explanation:

tyrone travels 30 miles in 58.2 minutes.  

1 mile = 5280 feet; this means he travels

30(5280) = 158400 feet in 58.2 minutes.

1 minute = 60 seconds; this means he travels 158400 feet in

58.2(60) = 3492 seconds.

this gives us the unit rate of

158400/3492 = 45.36 feet per second.