The answer is square root 6/2
D
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let n be the number of times letter be found (1800), p be the success rate (0.068), and q be the failure rate (1 - 0.068 = 0.932)
mean = np = 1800 x 0.068 = 122.4
standard deviation = √(npq) = √(1800 x 0.068 x 0.932) = 10.6807414
The third option is the right one
X=36 because 1/3 times 36 equals 12