I am going to assume the cards are replaced each time.
Let x be the number of blue and 60-x be the number of red
P(at least 2 red) >=0.5
P(0 or 1 red) <=0.5
P(all blue)+P(1R and 5 blue) <=0.5
$$\\\frac{x^6}{60^6}+6C1\left[\frac{(60-x)}{60}\right]^1\left[\frac{x}{60}\right]^5\le0.5\\\\\\
\frac{x^6}{60^6}+6\left[\frac{(60-x)x^5}{60^6}\right]\le0.5\\\\\\$$
I used Wolfram|Alpha to solve this
http://www.wolframalpha.com/input/?i=%28x^6%2F60^6%29%2B6*%28%28%2860-x%29*x^5%29%2F60^6%29%3C0.5
$$\\x\le44\\\\
$So the must be less than 44 or equal to 44 blue cards$\\\\
$Which means that there must be 16 or more red cards.$ \\\\$$
check:
$$\frac{44^6}{60^6}+\frac{6*(60-44)*44^5}{60^6} = 0.4949$$ seems alright ![]()
@@ End of Day Wrap Sat 28/3/15 Sydney, Australia Time 9:55 am ♪ ♫
Hi all,
Great answers today from Falkirks, TayJay, Civonumzuk, Alan, Heureka, CPhill, Geno3141 and BrittanyJ.
Thank you ![]()
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