document.write( "Question 1189201: A discrete random variable X has probability mass function P(x) = a(2/5)^x, x=0,1,2,3... Find the value of a. \n" ); document.write( "
Algebra.Com's Answer #820494 by ikleyn(52797)\"\" \"About 
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document.write( "The sum of the infinite geometric progression  P(0) + P(1) + P(2) + . . .  must be equal to 1.  It gives an equation to find \"a\".\r\n" );
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document.write( "The sum is equal to  \"a%2F%281-2%2F5%29\" = \"a%2F%28%283%2F5%29%29\" = \"%285a%29%2F3\".\r\n" );
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document.write( "So,  \"%285a%29%2F3\" must be equal to 1\r\n" );
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document.write( "    \"%285a%29%2F3\" = 1,\r\n" );
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document.write( "which gives  a = \"3%2F5\" = 0.6.    ANSWER\r\n" );
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