The question is incomplete! Complete question along with answer and step by step explanation is provided below.
Question:
The lifetime (in hours) of a 60-watt light bulb is a random variable that has a Normal distribution with σ = 30 hours. A random sample of 25 bulbs put on test produced a sample mean lifetime of = 1038 hours.
If in the study of the lifetime of 60-watt light bulbs it was desired to have a margin of error no larger than 6 hours with 99% confidence, how many randomly selected 60-watt light bulbs should be tested to achieve this result?
Given Information:
standard deviation = σ = 30 hours
confidence level = 99%
Margin of error = 6 hours
Required Information:
sample size = n = ?
Answer:
sample size = n ≈ 165
Step-by-step explanation:
We know that margin of error is given by
Margin of error = z*(σ/√n)
Where z is the corresponding confidence level score, σ is the standard deviation and n is the sample size
√n = z*σ/Margin of error
squaring both sides
n = (z*σ/Margin of error)²
For 99% confidence level the z-score is 2.576
n = (2.576*30/6)²
n = 164.73
since number of bulbs cannot be in fraction so rounding off yields
n ≈ 165
Therefore, a sample size of 165 bulbs is needed to ensure a margin of error not greater than 6 hours.
Answer:
Step-by-step explanation:
Given that,
y=x+2 equation 1
2x-y=-4 equation 2
This is a simultaneous equation.
Substitute equation 1 into equation 2
2x-y=-4. Since y=x+2
2x-(x+2) = -4
2x-x-2 = -4
x-2 = -4
x = -4+2
x = -2
Also from equation 1
y=x+2
Since x=-2
y=-2+2
y=0
Then, solution (x, y) = (-2,0)
Answer:
Step-by-step explanation:
Mixed fraction 
can be converted into like or unlike fractions.
Here, 
So, convert all the given fractions as follows:
Here, No Two fractions on addition gives a sum greater than 5.
But an approximate sum of 5 is given by adding 2.4 + 2.6 = 5
⇒
or ⇒
Answer:
1 over 8
Step-by-step explanation:
The point-slope form:
We have the points (-5, 15) and (20, 25). substitute:
Answer:
point-slope form: 
slope-intercept form: 
standard form: 
