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3 years ago

Jacob leaves his summer cottage and drives home. After

Mathematics

1 answer:

krok68 [10]3 years ago

6 0

Answer:

A linear relationship can be written as:

y = a*x + b

Where a is the slope and b is the y-intercept.

If this line passes through the points (a, b) and (c, d) then the slope can be written as:

a = (a - c)/(b - d)

Here y will represent the distance between Jacob and his house, and the variable x represents the time that he has ben driving.

In this case, we know that after driving for 5 hours, he is 112km from home.

Then we can write this point as (5h, 112km)

We also know that after 7 hours he is 15km from home.

Then we can write this point as (7h, 15km)

Then the slope of this function will be:

a = (15km - 112km)/(7h - 5h) = -48.5 km/h

Then the equation is:

y = -(48.5 km/h)*x + b

To find the value of b, we can replace the values of one of the points, for example in the point (7h, 15km)

This means that we need to replace x by 12h, and y by 15km, then we get:

15km = -( 48.5 km/h)*7h + b

15km + ( 48.5 km/h)*7h = b = 354.5 km

then the equation will be:

y = (-48.5 km/h)*x + 354.5 km

Now we want to answer: How long had Jacob been driving when he was 209 km from home?

Then we need to only replace y by 209km, and solve for x:

209km = (-48.5 km/h)*x + 354.5 km

209km - 354.5 km = (-48.5 km/h)*x

-145.5km = (-48.5 km/h)*x

-145.5km/( -48.5 km/h) = x = 3h

So he is 209km away from his home after driving for 3 hours.

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Read 2 more answers

In March 2015, the Public Policy Institute of California (PPIC) surveyed 7525 likely voters living in California. This is the 14

lbvjy [14]

Answer:

We are confident at 99% that the difference between the two proportions is between $0.380 \leq p_{Republicans} -p_{Democrats} \leq 0.420$

Step-by-step explanation:

Part a

Data given and notation

$X_{D}=3266$ represent the number people registered as Democrats

$X_{R}=2137$ represent the number of people registered as Republicans

$n=7525$ sampleselcted

$\hat p_{D}=\frac{3266}{7525}=0.434$ represent the proportion of people registered as Democrats

$\hat p_{R}=\frac{2137}{7525}=0.284$ represent the proportion of people registered as Republicans

The standard error is given by this formula:

$SE=\sqrt{\frac{\hat p_D (1-\hat p_D)}{n_{D}}+\frac{\hat p_R (1-\hat p_R)}{n_{R}}}$

And the standard error estimated given by the problem is 0.008

Part b

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

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".

$p_A$ represent the real population proportion of Democrats that approve of the way the California Legislature is handling its job

$\hat p_A =\frac{1894}{3266}=0.580$ represent the estimated proportion of Democrats that approve of the way the California Legislature is handling its job

$n_A=3266$ is the sample size for Democrats

$p_B$ represent the real population proportion of Republicans that approve of the way the California Legislature is handling its job

$\hat p_B =\frac{385}{2137}=0.180$ represent the estimated proportion of Republicans that approve of the way the California Legislature is handling its job

$n_B=2137$ is the sample for Republicans

$z$ represent the critical value for the margin of error

The population proportion have the following distribution

$p \sim N(p,\sqrt{\frac{p(1-p)}{n}})$

The confidence interval for the difference of two proportions would be given by this formula

$(\hat p_A -\hat p_B) \pm z_{\alpha/2} \sqrt{\frac{\hat p_A(1-\hat p_A)}{n_A} +\frac{\hat p_B (1-\hat p_B)}{n_B}}$

For the 90% confidence interval the value of $\alpha=1-0.90=0.1$ and $\alpha/2=0.05$ , with that value we can find the quantile required for the interval in the normal standard distribution.

$z_{\alpha/2}=1.64$

And replacing into the confidence interval formula we got:

$(0.580-0.180) - 1.64 \sqrt{\frac{0.580(1-0.580)}{3266} +\frac{0.180(1-0.180)}{2137}}=0.380$

$(0.580-0.180) + 1.64 \sqrt{\frac{0.580(1-0.580)}{3266} +\frac{0.180(1-0.180)}{2137}}=0.420$

And the 99% confidence interval would be given (0.380;0.420).

We are confident at 99% that the difference between the two proportions is between $0.380 \leq p_{Republicans} -p_{Democrats} \leq 0.420$

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