Question

If three coins are tossed, what are the mean, variance, and standard deviation of the number of heads that occur?

Answer 1

The number of heads is $X\sim Bin(3,0.5)$

Hence

$EX=3\cdot 0.5=1.5\\ DX=3\cdot 0.5 \cdot (1-0.5)=0.75\\ \sigma X=\sqrt{DX}=0.866$