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3 years ago

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32 envelopes + 15 postcards = $47.11

1 answer:

sweet [91]3 years ago

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See photo

Hope it helps

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The mean life of a particular brand of light bulb is 1200 hours. If you know that at about 95% of this brand of bulbs will last

Pachacha [2.7K]

Answer:

c) 50

Step-by-step explanation:

We have been given that the mean life of a particular brand of light bulb is 1200 hours. About 95% of this brand of bulbs will last between 1100 and 1300 hours.

We will use z-score formula to solve our given problem.

$z=\frac{x-\mu}{\sigma}$ , where,

$z=\text{z-score}$ ,

$x=\text{Sample score}$ ,

$\mu=\text{Mean}$ ,

$\sigma=\text{Standard deviation}$

We know that 95% of data points lies within two standard deviation of mean, so 1100 will correspond to a z-score of -2 and 1300 will correspond to a z-score of 2.

$-2=\frac{1000-1200}{\sigma}$

$-2=\frac{-100}{\sigma}$

$\sigma=\frac{-100}{-2}$

$\sigma=50$

We can use sample score 1300 and get same answer as:

$2=\frac{1300-1200}{\sigma}$

$2=\frac{100}{\sigma}$

$\sigma=\frac{100}{2}$

$\sigma=50$

Therefore, the standard deviation of the light bulbs’ life is 50 years.

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4 years ago