Question 1191825
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In a box containing 13 red balls, 9 green balls and 7 yellow balls. 
Two balls are drawn one by one without replacement, what is the probability that
(correct your answers to 4 decimal places.)
(a) both of them are the same color?
(b) both of them are not green?
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In all, there are 13 + 9 + 7 = 29 balls.


<pre>
(a)  P = P(RR) + P(GG) + P(YY) = {{{(13/29)*(12/28) + (9/29)*(8/28) + (7/29)*(6/28)}}} = {{{(13*12 + 9*8 + 7*6)/(29*28)}}} = 

       = {{{270/812}}} = {{{135/406}}} = 0.3325  (rounded).    <U>ANSWER</U>



(b)  P = {{{((13+7)/29)*((13+7-1)/28)}}} = {{{(20/29)*(19/28)}}} = {{{380/812}}} = {{{95/203}}} = 0.4680  (rounded).    <U>ANSWER</U>
</pre>

Solved.


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If you are wondering why there is a difference between my answer for part (a) and that by the other tutor,

it is because there is an error in calculations by @greenestamps in P(GG).