Find the standard deviation of the random variable.?

In a box of 10 batteries, 8 are dead. You choose two batteries at random from the box.


Let the random variable X be the number of good batteries you get. Find the standard deviation of of X.








a. = 0.53





b. = 0.51





c. = 0.32





d. = 0.28





e. = 0.65

Find the standard deviation of the random variable.?
Number your batteries from zero to nine.


Here are the possible picks from the box.


.. 01 02 03 04 05 06 07 08 09


10 .. 12 13 14 15 16 17 18 19


20 21 .. 23 24 25 26 27 28 29


30 31 32 .. 34 35 36 37 38 39


40 41 42 43 .. 45 46 47 48 49


50 51 52 53 54 .. 56 57 58 59


60 61 62 63 64 65 .. 67 68 69


70 71 72 73 74 75 76 .. 78 79


80 81 82 83 84 85 86 87 .. 89


90 91 92 93 94 95 96 97 98 ..


Hope this helps, I'll edit it if I learn more.


OKAY, THE ANSWER IS A.) 0.533333


I just did the whole thing on paper.


0.4^2 + 0.6^2 + 1.6^2 is 12.80 and divide by 45


to get 0.284444 and square root to get 0.53333


The mean is 0.4


and there are 28 zeros that are 0.4 away.


and there are 16 ones that are 0.6 away.


and there is one two that is 1.6 away from the mean, because 2 minus 0.4 is 1.6


See?
Reply:x = 2 prob. 1/10 then the mean= 0.2





variance = 0.4 - 0.04 =0.36





standard deviation = 0.6