-2/3-(-1 1/3) =
-2/3 + 1 1/3 =
4/3 - 2/3 =
<em>2/3</em>
12 - (-5) =
12 + 5 =
<em>17</em>
-1 - (-6) =
-1 + 6 =
6 - 1 =
<em>5</em>
-3 3/8 - 7/8 =
27/8 - 7/8 =
20/8 =
2 4/8 =
<em>2</em><em> </em><em>1/2</em>
4 pairs of shoes cost $80. What is the cost of 7 pairs of shoes?
2 answers:
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Answer:
A
Step-by-step explanation:
The constant of proportionality is the ratio between the two proportional variables in a directly proportional relationship. In this case, the variables are and
.
To find the constant of proportionality, all we have to do is divide any value of by its corresponding value of
. Let's take the values in the first row of the table. We know that
and
, so the constant of proportionality is
. Hope this helps!
We assume the lunch prices we observe are drawn from a normal distribution with true mean and standard deviation 0.68 in dollars.
We average samples to get
.
The standard deviation of the average (an experiment where we collect 45 samples and average them) is the square root of n times smaller than than the standard deviation of the individual samples. We'll write
Our goal is to come up with a confidence interval (a,b) that we can be 90% sure contains .
Our interval takes the form of as
is our best guess at the middle of the interval. We have to find the z that gives us 90% of the area of the bell in the "middle".
Since we're given the standard deviation of the true distribution we don't need a t distribution or anything like that. n=45 is big enough (more than 30 or so) that we can substitute the normal distribution for the t distribution anyway.
Usually the questioner is nice enough to ask for a 95% confidence interval, which by the 68-95-99.7 rule is plus or minus two sigma. Here it's a bit less; we have to look it up.
With the right table or computer we find z that corresponds to a probability p=.90 the integral of the unit normal from -z to z. Unfortunately these tables come in various flavors and we have to convert the probability to suit. Sometimes that's a one sided probability from zero to z. That would be an area aka probability of 0.45 from 0 to z (the "body") or a probability of 0.05 from z to infinity (the "tail"). Often the table is the integral of the bell from -infinity to positive z, so we'd have to find p=0.95 in that table. We know that the answer would be z=2 if our original p had been 95% so we expect a number a bit less than 2, a smaller number of standard deviations to include a bit less of the probability.
We find z=1.65 in the typical table has p=.95 from -infinity to z. So our 90% confidence interval is
in other words a margin of error of
dollars
That's around plus or minus 17 cents.