# Statistics with Probability

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• #13261

A 6 sided dice is rolled 1000 times. Let be random variable which consists of 1 if a roll is 1 and 0 otherwise. Let X be the random variable which counts the number of 1’s in the 1000 rolls.
a) Find expectation for and X and interpret.
b) Find standard deviation for and X and interpret.

#16817

See attachment for solution

#16834

I found out another way to do standard deviation is the square root of n * p * q with q=1-p. This was helpful for the standard deviation of E[x] since it was harder to find than E[Xi]

#16846

you can also get the variance of Xi by doing Var(Xi)= p(1-p) which is
1/6(1-(1/6))= (1/6)(5/6) then that gives you 5/36 and when you take the square root of that to find the Sd you get .37
easy and straight to the point

#16862

ok thats useful

#16892

It’s 3 in the morning…this is dreadful. Here, I believe this is more straight forward.

#16900

for the last part: V[X} you forgot to multiply by 1000 so it’s going to be
1000* 1/6 * 5/6 = 138.8889
SD+ sqrt(138.889) = 11.78

#16901

No, you don’t multiply. Divide. Pretty certain about that.

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