Selection round 2019 Mymensingh Higher Secondary #2

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samiul_samin
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Selection round 2019 Mymensingh Higher Secondary #2

Unread post by samiul_samin » Mon Jan 21, 2019 11:26 pm

There are $3$ white balls,$4$ green balls and $5$ red balls in a box.If yourandomly pick $3$ balls from the box,the probablity of picking $2$ white balls and $1$ red ball is $\dfrac{a}{b}$.What is the value of $a+b$ where $a$ and $b$ are co-prime?
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samiul_samin
Posts:1007
Joined:Sat Dec 09, 2017 1:32 pm

Re: Selection round 2019 Mymensingh Higher Secondary #2

Unread post by samiul_samin » Mon Jan 21, 2019 11:30 pm

Answer
$\fbox {47}$
Solution

$\dfrac{a}{b}=\dfrac{\binom{3}{2}×\binom{5}{1}}{\binom{12}{3}}=\dfrac{3}{44}$

$a+b=47$
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