Half life is the time taken for half a quantity of a substance to decay . fermium (atomic number 100 ) has 19 isotopes , most of which have half-lives if less than a second .

from the Fermium 257, he's got 100Kgs of Fermium 252, and Fermium 253.

the 252 is 40%, well, 40% of 100 is just 40, so 40 of Fermium 252, with a half-life of 1 day.

and 60% of 100 is just 60, so 60Kgs of Fermium 253 with a half-life of 3 days.

from August 31st to September 15, that'd be 15 days later, so how much is left altogether after 15 days.

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'.