Probability problem without replacement

[lawlercaust]

R0 R0 R1 R1 R2 G0 G0 G2 B0 B2

Two balls are drawn at random without replacement. What is the probability
that the sum of the numbers on the two balls is 1?

The answer is 20/90 but what is the procedure to solve this problem?

Probably of First Draw:
1 - (8/10) = 2/10
Probability of Second Draw:
1 - (6/8) = 2/8

 

[The Chaz]

Procedure:
List the possible ways to get a sum of "2".
a) 0 + 2
b) 1 + 1
Each of these has its own probability. Find them and add them.

 

[awkward]

R0 R0 R1 R1 R2 G0 G0 G2 B0 B2

Two balls are drawn at random without replacement. What is the probability
that the sum of the numbers on the two balls is 1?

The answer is 20/90 but what is the procedure to solve this problem?

Probably of First Draw:
1 - (8/10) = 2/10
Probability of Second Draw:
1 - (6/8) = 2/8

To get a total of 1 you must either draw 0 then 1, or 1 then 0.

P(0 then 1) = (5/10) (2/9)

and P(1 then 0) = (2/10) (5/9)

 

[The Chaz]

Procedure:
List the possible ways to get a sum of "2".
a) 0 + 2
b) 1 + 1
Each of these has its own probability. Find them and add them...

...and that's not what you were asking! Unless that's what your EDIT was about