I think the best thing to do here is to construct a diagram. The problem gives you vertices with coordinates from the Cartesian plane, and it even gives you an inequality. Here is the construction I created. I will reference it throughout the solving process:
I first located the given coordinates and connected them with vertical and horizontal lines. I then graphed the inequalityx>7y, which can be rewritten as y<x7 . I added a few points, as they will become relevant when I solve.
One way to solve this problem is to figure out the ratio of the area created by the inequality y<x7 and the sides of the rectangle to the area of the entire rectangle. I will do this by first finding the coordinates of the point E. Point E is located on ¯BC , so its x-coordinate is also 2009. If you know the x-coordinate, then the y-coordinate of any point on y=x7 is x7 . Therefore, the y-coordinate is 20097 .
The formula for the area of the triangle is 12bh . △ABE is a right triangle, so the base and height are the side lengths that are not the hypotenuse. We know the length of the base, AB , because it is in the diagram. The height is the length of BE , or 20097
A△=12∗AB∗BE=12∗2009∗20097=2009214
We can also calculate the area of the rectangle
Arect.=bh=AB∗BC=2009∗2010
As aforementioned, the probability of (x,y) such that x>7y is just the ratio of these areas.
P(x,y|x>7y)=A△Arect. | As aforementioned, the probability of (x,y) such that x>7y is just the ratio of these areas. Substitute in the values and simplify. |
P(x,y|x>7y)=20092142009∗2010 | Use algebraic manipulation to simplify this. |
P(x,y|x>7y)=2009214∗2009∗2010 | |
P(x,y|x>7y)=200914∗2010 | At this point, you must use a calculator. |
P(x,y|x>7y)=0.07139 | |
I think questions like this one are always really hard to understand and I would like another mathematician to check my answer.
Use my pic, which is near enough to the same.
Think about a horizontal line through the graph.
At the top it will pass through the graph twice so g(c)=2
Here is a pic
I have drawn six horizonal lines.
For the top (purple - 1st ) one f(x)=-2
this crosses the graph f(x) at 2 different x values so g(-2)=2
the next horizontal line (black 2nd ) palsses through 4 points so g(-2.8)=4
the 3rd horizontal line (red ) palsses through 6 points so g(-3.4)=6
the 4th horizontal line (blue ) palsses through 5 points so g(-4)=5
the 5th horizontal line (green) palsses through 4 points so g(-5)=4
the bottom horizontal line (purple ) palsses through 2 points so g(-6.7)=2
So g(c) can be 2, 4, 5, or 6
The average of the distict values of g(c) = (2+4+5+6)/4 = 17/4 = 4.25
I am pretty sure that is correct.
Here is the graph I used https://www.desmos.com/calculator/ft9bo78w4l
You do not need it though.