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aliina [53]
2 years ago
8

Eighteen individuals who use a particular form of social media were assigned a new user interface to use when logging into their

accounts. after using the new user interface for a week, each individual was asked to rate how easy or hard the new user interface was to use on a scale from 1 (extremely easy) to 9 (extremely hard). which of the following correctly identifies why this is not a well designed experiment?
A. There was a lack of control because not all individuals in the study used login passwords of the same length

B. The individuals may not have been randomly selected

C. There was not enough replication because the individuals used the new user interface for only one week.

D. there was a lack of control because not all individuals in the study use social media

E. the study was not comparative- only one treatment was used.
Mathematics
2 answers:
lianna [129]2 years ago
5 0

Answer:

Answer E . The study was not comparative—only one treatment was used.

Step-by-step explanation:

Well-designed experiments should involve comparisons of at least two treatment groups, one of which could be a control group.

Lisa [10]2 years ago
3 0

Answer:

E: The study was not comparative—only one treatment was used.

Step-by-step explanation:

Well-designed experiments should involve comparisons of at least two treatment groups, one of which could be a control group.

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7400 dollars is placed in an account with an annual interest
Anastasy [175]

Answer:

17

Step-by-step explanation:

We have the following equation for compounding annual interest

AV=PV(1+i)ⁿ

We have

19200=7400(1+.06)ⁿ

Solve for n

divide both sides by 7400

2.594=(1.06)ⁿ

then use the following rule for exponents

x^y=z\\log_xz=y

which means that

log_{1.06}2.594=n

Solve and get

16.362

which rounds to 17

6 0
3 years ago
Find the cost of 10 pens at x pence each
Reika [66]

Answer:

D. x + 10 pence

Step-by-step explanation:

Since the pen costs 10 pence more than the ruler, we need to add 10 to x.

6 0
2 years ago
Read 2 more answers
SAT scores are normed so that, in any year, the mean of the verbal or math test should be 500 and the standard deviation 100. as
vovangra [49]

Answer:

a) P(X>625)=P(\frac{X-\mu}{\sigma}>\frac{625-\mu}{\sigma})=P(Z>\frac{625-500}{100})=P(Z>1.25)

P(Z>1.25)=1-P(Z

b) P(400

P(-1

P(-1

c) z=-0.842

And if we solve for a we got

a=500 -0.842*100=415.8

So the value of height that separates the bottom 20% of data from the top 80% is 415.8.  

Step-by-step explanation:

Previous concepts

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  

Part a

Let X the random variable that represent the SAT scores of a population, and for this case we know the distribution for X is given by:

X \sim N(500,100)  

Where \mu=500 and \sigma=100

We are interested on this probability

P(X>625)

And the best way to solve this problem is using the normal standard distribution and the z score given by:

z=\frac{x-\mu}{\sigma}

If we apply this formula to our probability we got this:

P(X>625)=P(\frac{X-\mu}{\sigma}>\frac{625-\mu}{\sigma})=P(Z>\frac{625-500}{100})=P(Z>1.25)

And we can find this probability using the complement rule and with the normal standard table or excel:

P(Z>1.25)=1-P(Z

Part b

We are interested on this probability

P(400

And the best way to solve this problem is using the normal standard distribution and the z score given by:

z=\frac{x-\mu}{\sigma}

If we apply this formula to our probability we got this:

P(400

And we can find this probability with this difference:

P(-1

And in order to find these probabilities we can find tables for the normal standard distribution, excel or a calculator.  

P(-1

Part c

For this part we want to find a value a, such that we satisfy this condition:

P(X>a)=0.8   (a)

P(X   (b)

Both conditions are equivalent on this case. We can use the z score again in order to find the value a.  

As we can see on the figure attached the z value that satisfy the condition with 0.2 of the area on the left and 0.8 of the area on the right it's z=-0.842. On this case P(Z<-0.842)=0.2 and P(Z>-0.842)=0.8

If we use condition (b) from previous we have this:

P(X  

P(z

But we know which value of z satisfy the previous equation so then we can do this:

z=-0.842

And if we solve for a we got

a=500 -0.842*100=415.8

So the value of height that separates the bottom 20% of data from the top 80% is 415.8.  

8 0
2 years ago
Elisa ​says, "If you subtract 14 from my number and multiply the difference by -3 ​, the result is -33 ​." What is Elise​'s ​num
Svetach [21]

Answer:

25

Step-by-step explanation:

(x-14)*-3 = -33

-3x+42 = -33

-3x = -33-42

-3x = -75

x=25

6 0
2 years ago
X subtract 9 equals 3 / 5X
Korvikt [17]

Answer:

x=22\frac{1}{2}=22.5

Step-by-step explanation:

x-9=\frac{3}{5}x

  • First, lets get rid of the fraction. I did this by multiplying both sides by 5.

5(x-9)=5(\frac{3}{5}x)\\5x-45=\frac{5}{1} *\frac{3}{5}x\\5x-45=\frac{15}{5}x\\5x-45=3x

  • We want to isolate x on one side of this equation. Let's put any values with x on one side of the equation, and normal integers on the other.

2x=45

  • Divide both sides by 2.

x=\frac{45}{2}

  • If your teacher wants you to leave your final answer as an improper fraction, your final answer is this. If they want it to be a mixed number or decimal, your final answer will be:

x=22\frac{1}{2}=22.5

7 0
3 years ago
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