# Probability question?

Question:Two bags each contain 5 balls numbered 1-5. If one ball is taken randomly from each bag, what is the probability that the sum of the numbers on the 2 balls will be 9?

1/25 , 2/25, 1/9, 2/9

1,1
1,2
1,3
1,4
1,5
2,1
2,2
.
5,5
25 possibilities
how many of these add up to 9?
4,5 or 5,4
2/125
You need information on combinations and permutations. Do a google search (and look in your math book).

I'll give you a hint for the numerator... if you only have the numbers 1 - 5, which numbers add together to make nine? If I grab a four out of one bag, what do I HAVE to get from the other bag to get a sum of 9?
P(9) = P(5 and 4) or P(4 and 5)
= 1/5*1/5 + 1/5*1/5
=1/25 + 1/25
=2/25

Hope this helps
1/25?...
There are only 2 cases which the sum is 9.
Case 1: 1st ball is numbered 4 and 2nd ball is numbered 5
Probability = 1/5 x 1/5 = 1/25

Case 2: 1st ball is numbered 5 and 2nd ball is numbered 4
Probability = 1/5 x 1/5 = 1/25

Therefore, the chance such an occurance can happen is
1/25 + 1/25 = 2/25 (ans)
The best way to see this problem is to draw a table. let the first row be the ball from bag 1 and the first column be the ball from the second bag. the elements of the table are the sum of the two balls.

____1__2__3__4__5_
_1__2__3__4__5__6_
_2__3__4__5__6__7_
_3__4__5__6__7__8_
_4__5__6__7__8__9_
_5__6__7__8__9__10

There are a total 25 possible outcomes and only two of those outcomes sum to 9. So assuming that each ball has the probability of being drawn the solution is 2/25.

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