A bag contains 100 marbles which are red, green, and blue. Suppose a student randomly selects a marble without looking, records the color, and then places the marble back in the bag. The student has recorded 7 red marbles, 2 green marbles and 11 blue marbles. Predict how many green marbles are in the bag.

80

Step-by-step explanation:

If the bag has 100 marbles and 7+2+11=20 then you subtract what you got adding the quantities you already know from the total, and you have your answer :D

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.

sounds & other waves originate from any vibrating object