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2 years ago

What is it that I do with my life that will help me be better person

Mathematics

1 answer:

MakcuM [25]2 years ago

3 0

Listen to peoples problems, care about them and give advices.

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Suppose the standard deviation of X is 6 and the standard deviation of Y is 8. Answer the following two questions, rounding to t

Darina [25.2K]

Recall that

Var[aX + bY] = a ² Var[X] + 2ab Cov[X, Y] + b ² Var[Y]

Then

Var[3X - 7Y] = 9 Var[X] - 42 Cov[X, Y] + 49 Var[Y]

Now, standard deviation = square root of variance, so

Var[3X - 7Y] = 9×6² - 42×2 + 49×8² = 3376

The general result is easy to prove: by definition,

Var[X] = E[(X - E[X])²] = E[X ²] - E[X]²

Cov[X, Y] = E[(X - E[X]) (Y - E[Y])] = E[XY] - E[X] E[Y]

Then

Var[aX + bY] = E[((aX + bY) - E[aX + bY])²]

… = E[(aX + bY)²] - E[aX + bY]²

… = E[a ² X ² + 2abXY + b ² Y ²] - (a E[X] + b E[Y])²

… = E[a ² X ² + 2abXY + b ² Y ²] - (a ² E[X]² + 2 ab E[X] E[Y] + b ² E[Y]²)

… = a ² E[X ²] + 2ab E[XY] + b ² E[Y ²] - a ² E[X]² - 2 ab E[X] E[Y] - b ² E[Y]²

… = a ² (E[X ²] - E[X]²) + 2ab (E[XY] - E[X] E[Y]) + b ² (E[Y ²] - E[Y]²)

… = a ² Var[X] + 2ab Cov[X, Y] + b ² Var[Y]

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3 years ago

Using substitution, which value of x makes this equation true?

KiRa [710]

Answer:

The answer is B. 7

Step-by-step explanation:

3 + x = 10

3 + 7 = 10

7 0

3 years ago

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Carol spends 17 hours in a 2-week period practicing her culinary skills. How many hours does she practice in 5 weeks?

LekaFEV [45]

Answer:

42 and a half

Step-by-step explanation:

17÷2 = 8.5x5= 42.5(42 and a half)

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3 years ago

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PLEASE HELP ITS OVERDUE PLEASE I NEED HELP!!

IgorLugansk [536]

Answer:

First question: Choice A

second question:Choice D

Third question: Choice c

Fourth question: Choise b

5th Question: choice b

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3 years ago

Vermont had 3 inches of snow on the ground before the sun melted 2 inches. The next storm tripled the amount on the ground. The

Finger [1]

The answer to the question is 2 and 1/2 left on the ground.

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3 years ago