Answer:

And we can find this probability using the normal standard table or excel and we got:

The figure shows the calculation for this case.
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".
Solution to the problem
Let X the random variable that represent the hardness of a population, and for this case we know the distribution for X is given by:
Where
and 
We are interested on this probability

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

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

And we can find this probability using the normal standard table or excel and we got:

The figure shows the calculation for this case.
Answer:
Step-by-step explanation:
The total number of marbles is 20
Question A
P(Red) = 4/20 = 1/5
P(yellow) = 9/20
P(Red then Yellow) = 1/5 * 9/20 = 9 / 100
Question B
P(B) = 6/20
P(B again) = 5/19 because you have 1 less total plus 1 less blue.
P(B and B) = 6/20 * 5/19
P(B and B) = 30/ 380 = 3/38
Answer:
A
Step-by-step explanation:
Using Pythagoras theorem, we have
x^2+11^2=15^2, x^2=104, x=2*sqrt(26)
Answer:
y = x+2
Step-by-step explanation:
(x1,y1) is (-4,-2) and (x2,y2) is (2,4)
Slope intercept form is y = mx+b
m = slope
b = add on
Slope = 
Substitute numbers
Slope = 
Two negatives = one positive
Simplify

The slope is 1
We can substitute y, x, and the slope
4 = 2*1 + b
4 = 2+b
b = 2
Slope intercept form is y = mx+b
Answer is y = x+2
Hope this helps :)
we are given
In A 4 year period, About 80,000 acres of coastal wetlands in United States are lost each year.
so, total area =80000 acres
total time = 4 years
now, we can use formula
total change in wetlands = ( total area)/(total time)
now, we can plug values
total change in wetlands is

................Answer