Question

Find the probability of at least 2 girls in 8 births. assume that male and female births are equally likely and that the births are independent events.

Answer 1

At least two girls means either 2, 3 ... or 8 girls. 
Using the binomial law, we can write the probability in the form:
B(2,0.5)+B(3,05)+...+B(8,0.5)=$0.0039(C_8^2+...+C_8^8)$
Continue simplifying:
$C_8^2+...+C_8^8=2^8-C_8^1=2^8-8=248\\\text{We deduce the probability of the event "at least two girls in birth ":}\\0.0039\times248=0.96\\\text{The above probability (0.96) means that the event is very likely}$