in class of 80 student debre berhan university ,45 are good in mathematics,15 are good in both mathematics and in english,13 are good in both mathematics and psychology,16 are good in both english and psychology only,20 are good in psychology and 9 are good in both of three courses. how many students are good in mathematics only ? how many students are not good in any of three courses ?

the answer   is 200

step-by-step explanation:

this is a problem about poisson probabilities.   i don't know if you've

already studied poisson distributions, or if you have a place to look

to read more about the subject.  

here's how you can see a poisson distribution coming.   when there are

a lot of events that may happen at any time (or any place), and when

you're counting how many of them happen at a particular time (or a

particular place), and each event is independent of the others, then

the result is a poisson distribution.   this is roughly true for the

chocolate chips; one chip being in a cookie has only a small effect on

the probability that another chip will be in the cookie.

once you know you have a poisson distribution, you know a lot.   there

is only one parameter to a poisson distribution, so if you know the

mean, you know everything.   the form of the distribution is

  probability of n chips = {[e^(-x)]*(x^n)} / (n! )

true

explanation:

the answer is (4,3)

since the rule for r0, 90º is (-y,x) and it was already applied to form the image, all you have to do is reverse the answer using this formula.

i believe it is c.y = 9x

rise over run. 9 units up over 1 unit right or 9/1