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ira [324]
3 years ago
11

The mean time it takes to walk to the bus stop is 8 minutes (with a standard deviation of 2 minutes) and the mean time it takes

for the bus to get to school is 20 minutes (with a standard deviation of 4 minutes). the distributions are normal.
a. how long will it take (in minutes), on average, to get to school?

b. what is the standard deviation of the trip to school?

c. what is the probability that it will take longer than 30 minutes to get to school? due to a miscalculation, you realize it actually takes an average of 10 minutes to walk to the bus stop.

d. how long will it take (in minutes), on average, to get to school?

e. what is the standard deviation of the trip to school? f. what is the probability that it will take longer than 30 minutes to get to school
Mathematics
1 answer:
11111nata11111 [884]3 years ago
8 0
(a) Average time to get to school
Average time (minutes) = Summation of the two means = mean time to walk to bus stop + mean time for the bust to get to school = 8+20 = 28 minutes

(b) Standard deviation of the whole trip to school
Standard deviation for the whole trip = Sqrt (Summation of variances)

Variance = Standard deviation ^2
Therefore,
Standard deviation for the whole trip = Sqrt (2^2+4^2) = Sqrt (20) = 4.47 minutes

(c) Probability that it will take more than 30 minutes to get to school
P(x>30) = 1-P(x=30)
Z(x=30) = (mean-30)/SD = (28-30)/4.47 ≈ -0.45
Now, P(x=30) = P(Z=-0.45) = 0.3264
Therefore,
P(X>30) = 1-P(X=30) = 1-0.3264 = 0.6736 = 67.36%

With actual average time to walk to the bus stop being 10 minutes;

(d) Average time to get to school
Actual average time to get to school = 10+20 = 30 minutes

(e) Standard deviation to get to school
Actual standard deviation = Previous standard deviation = 4.47 minutes. This is due to the fact that there are no changes with individual standard deviations.

(f) Probability that it will take more than 30 minutes to get to school
Z(x=30) = (mean - 30)/Sd = (30-30)/4.47 = 0/4.47 = 0

From Z table, P(x=30) = 0.5
And therefore, P(x>30) = 1- P(X=30) = 1- P(Z=0.0) = 1-0.5 = 0.5 = 50%
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<h3>Answer: Distance between x intercepts is 1 unit.</h3>

======================================================

Explanation:

Let's find the x intercept of f(x). Replace f(x) with 0 and solve for x

f(x) = -2x+2

0 = -2x+2

2x = 2

x = 2/2

x = 1

Plugging x = 1 into f(x) leads to f(x) = 0. The x intercept of f(x) is 1.

-----------------------

Now onto g(x). If we were given a row that had y = 0, then we'd immediately find the x intercept. However, that isn't given, so we'll have to do a bit of work to find the equation for g(x).

First we need the slope. Pick any two rows to find the slope. I'll pick the middle two rows.

m = (y2-y1)/(x2-x1)

m = (3-6)/(1-0)

m = -3/1

m = -3 is the slope

The y intercept is b = 6 as the table shows this pairs with x = 0. The y intercept always happens when x = 0.

So with m = -3 and b = 6, we see that g(x) = -3x+6.

-------------------------

Plug in g(x) = 0 and solve for x. We'll use similar ideas done in the first section at the very top

g(x) = -3x+6

0 = -3x+6

3x = 6

x = 6/3

x = 2 is the x intercept of g(x)

--------------------------

In summary, we found...

  • x = 1 is the y intercept of f(x)
  • x = 2 is the y intercept of g(x)

Subtract the x intercept values to get 2-1 = 1, which is the distance between the x intercepts. The distance is never negative.

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