Un número consta de dos cifras cuya suma es 9.Si se invierten el orden de las cifras el resultado es igual al número dado más 9 unidades. Encuentra dicho número.

45

Step-by-step explanation:

A number consists of 2 digits whose sum is 9 => x + y = 9

If the order of the numbers is inverted, the result is equal to the given number plus 9 units => (10*y + x) + 9 = (10*x + y)

Thus:

x + y = 9  => multiply by -9 => 9*y + 9*x = 81

10*y + x + 9 = 10*x + y =>  9*y - 9*x = -9

We are left then that:

9*y + 9*x = 81  (1)

9*y - 9*x = -9  (2)

we add both equations

18y = 72

y = 72/18 = 4

replacing

x + y = 9

x + 4 = 9

x = 5

Therefore the number is (10y + x) => (10 * 4 + 5) => 45

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! )