Logic maths: having fun 2

[gh0st]

In a lottery game are picked 6 balls of 20 which are enumerated from 1 to 20 ...
What is the probability to pick the firsts 2 balls which are going to sum 30?
for example they could be the ball 11 and 19 or 12 and 18...
alternatives:

hmm I think that the only numbers that can sum the cuantity of 30 are:
19,11 - 18,12 - 17,13 - 16,14
so I guess that what they are basicly asking to us is whats the probability to pick 2 numbers which are going to sum 30 so Idk the answer any ideas?
 

[Kreek]

Lol this isn't so hard...



In the blue zone is the picking of the first ball.. The chance of picking one of those is 1/20.
In the red zone is the picking of the second ball.. The chance of picking one of those is 1/19.
So when you combine them: ( (1/20) * (1/19 )) * 10 = 1/38 = 0.02631578947368421


I guess it's E then

[gh0st]

dude why do you multiply 1/20*1/19 ? and yes E is the answer gj

[Kreek]

dude why do you multiply 1/20*1/19 ? and yes E is the answer gj

If you want the chance when you first take number 10 and than number 20 you just need to multiply those two chances... Can't explain why, just a rule?

[7ate9]

Reason for multiplying (1/19) and (1/20) is because once one ball is chosen you only have 19 balls left to choose... Only 1 of the 19 will suffice, to equal the sum of 30.. hope that explanation helps..