Flood waters decreased in Death from 15 in to 8. In what was the percent decrease?
1 answer:
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Answer:
- A relationship modeled by the function f(x) = 4x³ - 72x² + 320x is the volume of a right prism whose dimensions are 4 times a desired length, 10 units less that such desired length, and 8 units less than the same desired length.
Explanation:
To find a relationship modeled by the given function it is recommendable to factor it.
The function is:
The first step to factor it is to extract common factor 4x:
The second step is to factor the quadratic trinomial.
That is made by writting it as a product of two binomials, for which the two constant terms add up - 18 and their product is 80. Those terms are -10 and - 8; so the two factors are (x - 10) and (x - 8), and the factored form is:
Then, a relationship modeled by that polynomial is the volume of right prism whose dimensions are 4 times a desired length, 10 units less that such desired length, and 8 units less than the same desired length.
- x is the desired (unknown) length
- 4x is 4 times the desired length
- x - 10 is 10 less than the desired length
- x - 8 is 8 less than the desired length
Thus, the volume of the prism is the product of the three factors:
- Volume = (4x)(x-10)(x-8)
What I gather from the question is that has second moment
and variance
, and you're asked to find the expectation and variance of the random variable
.
From the given second moment and variance, we find the expectation of :
Expectation is linear, so
Using the same variance identity, we have
and
so that
Alternatively, we can use the identity