Question 375368
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Hi,
Note: The probability of x successes in n trials is: 

P = nCx* {{{p^x*q^(n-x)}}} where p and q are the probabilities of success and failure respectively. 
In this case p & q are = 1/2 or .5
nCx = {{{n!/(x!(n-x!))}}}  4C3 = 4    4C4 = 1
P(x&#8805;3)= P(3) + P(4) 
P(3)=  4*(.5)^3(.5) = .25 
P(4)= .5^4 = .0625 
P(x&#8805;3)= .25 + .0625 = .3125