¿Cuál de los siguientes valores de n hace CIERTA

Paha777 [63]

$x^4 - 28x^2 = 0$

$x^2(x^2 - 28) = 0$

$x^2 = 0 \ \ or \ \ (x^2 - 28) = 0$

$x = 0 \ \ or \ \ x^2 = 28$

$x = 0 \ \ or \ \ x = \pm \sqrt{28}$

$x = 0 \ \ or \ \ x = \pm2 \sqrt{7}$

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Answer : x = 0 or 2√7 or -2√7
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8 0

3 years ago

Sally can paint a room in 9 hours while it takes Steve 3 hours to paint the same room. How long would it take them to paint the

Archy [21]

You can solve this one by adding their rates, but you have to invert the numbers they give you to find the rate. Rate is measured in something per unit of time, and "per" indicates division. So the rates are: 1/3 of an hour (Sally) and 1/6 of an hour (Steve). So add the rates: 1/3 + 1/6 = 1/2. (1/3 is 2/6, and 2/6 + 1/6 = 3/6). Since their combined rate is 1/2 of a room in one hour, it takes them two hours to paint the room.

This answer makes sense: It takes Sally three hours by herself; with Steve's help, she's faster, but not THAT much faster, because he's pretty slow. You can often spot-check word problem answers like this by giving it a common sense once-over. If we came up with four hours, that would clearly be wrong: it should take her LONGER if she's getting help.

7 0

3 years ago

Read 2 more answers

in chemistry class Andrew has earned scores of 64 69 and 73 on three tests he must maintain an average of 72

olganol [36]

You haven't told me what the question is. But I put the mouse
to my forehead, closed my eyes, took a deep breath, and I could
see it shimmering in my mind's eye. It was quite fuzzy, but I think
the question is

   "What score does Andrew need on the next test
   in order to raise his average to 72% ?"

The whole experience drew an incredible amount of energy
out of me, and the mouse is a total wreck. So we'll just go ahead
and answer that one. I hope it's the correct question.

The average score on 4 tests is

   (1/4) (the sum of all the scores) .

In order for Andrew to have a 72% average on 4 tests,
the sum of the 4 scores must be

   (4) x (72%) = 288% .

Out of that total that he needs, he already has

(64% + 69% + 73%) = 206%

on the first three tests.

So in order to average 72% for all 4 tests,
he'll need to score

   (288% - 206%) = 82%

on the fourth one.

6 0

3 years ago

Suppose there is a 13.9 % probability that a randomly selected person aged 40 years or older is a jogger. In addition, there is

Blababa [14]

Answer:

There is a 2.17% probability that a randomly selected person aged 40 years or older is male and jogs.

It would be unusual to randomly select a person aged 40 years or older who is male and jogs.

Step-by-step explanation:

We have these following probabilities.

A 13.9% probability that a randomly selected person aged 40 years or older is a jogger, so $P(A) = 0.13$ .

In addition, there is a 15.6% probability that a randomly selected person aged 40 years or older is male comma given that he or she jogs. I am going to say that P(B) is the probability that is a male. $P(B/A)$ is the probability that the person is a male, given that he/she jogs. So $P(B/A) = 0.156$

The Bayes theorem states that:

$P(B/A) = \frac{P(A \cap B)}{P(A)}$

In which $P(A \cap B)$ is the probability that the person does both thigs, so, in this problem, the probability that a randomly selected person aged 40 years or older is male and jogs.