document.write( "Question 1204025: An urn has 21 balls that are identical except that 5 are white, 9 are red, and 7 are blue. What is the probability that all are white if 3 are selected randomly without replacement?
\n" ); document.write( " \n" ); document.write( "
Algebra.Com's Answer #840026 by greenestamps(13198)\"\" \"About 
You can put this solution on YOUR website!


\n" ); document.write( "The response from tutor @ikleyn shows a solution using a more sophisticated (and more powerful) method. A student just beginning to study probability should understand a more elementary way of obtaining the answer for this relatively simple problem.

\n" ); document.write( "The more elementary method of solving the problem is to select the three balls one at at time and consider the probability that each one selected is white.

\n" ); document.write( "For the first ball, there are 21 balls to choose from of which 5 are white; the probability of getting a white ball is 5/21.
\n" ); document.write( "For the second ball, there are 20 balls to choose from of which 4 are white; the probability of getting a white ball is 4/20.
\n" ); document.write( "For the third ball, there are 19 balls to choose from of which 3 are white; the probability of getting a white ball is 3/19.

\n" ); document.write( "The probability of all three balls being white is then the product of those individual probabilities:

\n" ); document.write( "(5/21)(4/20)(3/19) = 1/133
\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );