document.write( "Question 998653: In seven given numbers, the average of first four numbers is 4 and that of the last four numbers is also 4. If the average of these seven numbers is 3, the fourth number is :\r
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Algebra.Com's Answer #616422 by ikleyn(52803) $\"\"$ $\"About$

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\n" ); document.write( "In seven given numbers, the average of first four numbers is 4 and that of the last four numbers is also 4. If the average of these seven numbers is 3, the fourth number is :
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document.write( "Since the average of first four numbers is  4,  the sum of first four numbers is  4*4 = 16:\r\n" );
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document.write( " +  +  +  = 16.           (1)\r\n" );
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document.write( "Since the average of the last four numbers is  4,  the sum of the last four numbers is  4*4 = 16:\r\n" );
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document.write( " +  +  +  = 16.           (2)\r\n" );
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document.write( "Add (1) and (2) and re-group. You will get\r\n" );
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document.write( "( +  +  +  +  +  + ) +  = 32.           (3)\r\n" );
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document.write( "Since the average of the seven numbers is  3,  their sum is  3*7 = 21:\r\n" );
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document.write( " +  +  +  +  +  +  = 21.\r\n" );
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document.write( "Comparing it with (3), you get  = 32 - 21 = 11.\r\n" );
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document.write( "Answer.  = 11.\r\n" );
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