The life of a manufacturer's compact fluorescent light bulbs is normal, with mean 12,000 hours and standard deviation 2,000 hour
2 answers:
Mean = 12000
Standard Deviation = 2000
We have to find how many standard deviations is 14,500 away from the mean.
This can be achieved by calculating the z-score
Z-score tells us how many standard deviations above or below is a sample value from the mean. A positive z value shows, sample value is above the mean.
z score can be calculated as = (Sample Value - Mean )/Standard Deviation)
So,
Z-score =
This means, 14,500 is 1.25 standard deviations above the mean value 12,000.
Standard Deviation = 2000
We have to find how many standard deviations is 14,500 away from the mean.
This can be achieved by calculating the z-score
Z-score tells us how many standard deviations above or below is a sample value from the mean. A positive z value shows, sample value is above the mean.
z score can be calculated as = (Sample Value - Mean )/Standard Deviation)
So,
Z-score =
This means, 14,500 is 1.25 standard deviations above the mean value 12,000.
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We'll use variables to represent the speeds of the eastbound and westbound trains.
x will represent the speed of the eastbound train.
y will represent the speed of the westbound train.
The eastbound train is 16 mph faster than the westbound train. An equation can be made from this:
Subtraction is used, because it represents the difference in distances between the two trains if they travel the same direction.
After 4 hours, the trains are 800 miles apart. An equation can be made from this:
Addition is used, because the trains are heading in opposite directions, which means their distances from the starting point are added together.
Set the two equations up vertically:
We will use elimination to solve for x.
Multiply the entire first equation by 4 so that the coefficients for y will be opposite numbers:
Combine the two equations together to cancel out y:
Divide both sides by 8 to get x by itself:
The speed of the eastbound train is 108 mph.
x will represent the speed of the eastbound train.
y will represent the speed of the westbound train.
The eastbound train is 16 mph faster than the westbound train. An equation can be made from this:
Subtraction is used, because it represents the difference in distances between the two trains if they travel the same direction.
After 4 hours, the trains are 800 miles apart. An equation can be made from this:
Addition is used, because the trains are heading in opposite directions, which means their distances from the starting point are added together.
Set the two equations up vertically:
We will use elimination to solve for x.
Multiply the entire first equation by 4 so that the coefficients for y will be opposite numbers:
Combine the two equations together to cancel out y:
Divide both sides by 8 to get x by itself:
The speed of the eastbound train is 108 mph.