SOLUTION: There are 9 sweets in a box. There are "n" jelly beans and the rest are cola bottles. Colin takes 2 sweets out of the box at random. Write an expression for the probability o

Question 1136068: There are 9 sweets in a box.
There are "n" jelly beans and the rest are cola bottles.
Colin takes 2 sweets out of the box at random.
Write an expression for the probability of getting 2 jelly beans.
Could you please help me with this question because I have never learnt this before in school and it is on my homework so please can someone help
I have no clue where to start
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
n jelly beans
9-n cola bottles
probability first is a jelly bean is (n/9)
probability second is also a jelly bean is now (n-1)/8 since there is one less sweet total and one less jelly bean
The product is n(n-1)/72 and that is the probability.
suppose there are 3 jelly beans and 6 cola bottles
then the probability is 3/9*2/8=1/12
n*(n-1)/72=6/72=1/12

Answer by ikleyn(52787) (Show Source): You can put this solution on YOUR website!
.

The answer is in TWO LINES:

if n < 2 then the probability under the question is 0 (zero, ZERO); otherwise (i.e. if n >= 2) the probability is = .

First line answer/option is clear, and I am sure, it does not require further explanations.

Second line answer/option is based on the fact, that at the first taking the probability to get a jelly bean is n of 9 items,
while the probability to get a jelly bean at the second taking is (n-1) of remaining 8 items.

The probabilities at the first and the second taking are INDEPENDENT EVENTS, so we multiply the probabilities of each event.

Congratulations: You obtained the full and complete solution with explanations.

Happy learning !

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