Answer:
standard error = 1.63
Step-by-step explanation:
To calculate the standard error we need to know the standard deviation (σ) and the sample size (n) (see the attached formula).
To obtain the standard deviation we use the given sample variance of 77.4 years:
σ²= variance
Therefore:
σ = √77.4 = 8.8
Now we can calcuate the estimated standard error:
standard error = σ /√n = 8.8/√29 = 1.63
The standard error gives us an estimation about how far the mean of the sample is from the mean of the entire population, and in this case is 1.63.
Given that mean=3750 hours and standard deviation is 300:
Then:
<span>a. The probability that a lamp will last for more than 4,000 hours?
P(x>4000)=1-P(x<4000)
but
P(x<4000)=P(z<Z)
where:
z=(x-</span>μ)/σ
z=(4000-3750)/300
z=0.833333
thus
P(x<4000)=P(z<0.8333)=0.7967
thus
P(x>4000)=1-0.7967=0.2033
<span>b.What is the probability that a lamp will last less than 3,000 hours?
P(x<3000)=P(z<Z)
Z=(3000-3750)/300
z=-2.5
thus
P(x<3000)=P(z<-2.5)=0.0062
c. </span><span>.What lifetime should the manufacturer advertise for these lamps in order that only 4% of the lamps will burn out before the advertised lifetime?
the life time will be found as follows:
let the value be x
the value of z corresponding to 0.04 is z=-2.65
thus
using the formula for z-score:
-2.65=(x-3750)/300
solving for x we get:
-750=x-3750
x=-750+3750
x=3000</span>
I think the answer might be x=24
Celculate the figures by using the numbers,with letters