Question 629925
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
{{{ten}}} true-or-false questions... student knows the correct answer to six of them
 P(scoring &#8805; 90%) = P(getting at least 3 of the remaining 4 correct)
 P(x&#8805;3) = P(3) + P(4) = 4C3(.5)^3(.5)^1 + 4C4(.5)^4 

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)!)}}}