document.write( "Question 823048: How many numbers lie between 300 and 500 in which 4 comes only one time? \n" ); document.write( "
Algebra.Com's Answer #496090 by Edwin McCravy(20056)\"\" \"About 
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How many numbers lie between 300 and 500 in which 4 comes only one time?
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document.write( "They are all of the form\r\n" );
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document.write( "\"4AB\", \"34B\", and \"3B4\", where A nor B is 4\r\n" );
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document.write( "Case 1:  The number of 3-digit numbers of type \"4AB\"\r\n" );
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document.write( "We can choose A as any of the 9 digits {0,1,2,3,5,6,7,8,9}\r\n" );
document.write( "We can choose B as any of the 9 digits {0,1,2,3,5,6,7,8,9}\r\n" );
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document.write( "So there are 9×9 = 81 ways for Case 1.\r\n" );
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document.write( "Case 2: The number of 3-digit numbers of type \"34B\"\r\n" );
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document.write( "We can choose B as any of the 9 digits {0,1,2,3,5,6,7,8,9}\r\n" );
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document.write( "So there are 9 ways for Case 2.\r\n" );
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document.write( "Case 3: The number of 3-digit numbers of type \"3B4\"\r\n" );
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document.write( "Same as Case 2: We can choose B as any of the 9 digits {0,1,2,3,5,6,7,8,9}\r\n" );
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document.write( "So there are 9 ways for Case 2.\r\n" );
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document.write( "Total 81+9+9 = 99\r\n" );
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document.write( "Here are all 99 in a 9 by 11 array:\r\n" );
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document.write( "304, 314, 324, 334, 340, 341, 342, 343, 345, 346, 347\r\n" );
document.write( "348, 349, 354, 364, 374, 384, 394, 400, 401, 402, 403\r\n" );
document.write( "405, 406, 407, 408, 409, 410, 411, 412, 413, 415, 416\r\n" );
document.write( "417, 418, 419, 420, 421, 422, 423, 425, 426, 427, 428\r\n" );
document.write( "429, 430, 431, 432, 433, 435, 436, 437, 438, 439, 450\r\n" );
document.write( "451, 452, 453, 455, 456, 457, 458, 459, 460, 461, 462\r\n" );
document.write( "463, 465, 466, 467, 468, 469, 470, 471, 472, 473, 475\r\n" );
document.write( "476, 477, 478, 479, 480, 481, 482, 483, 485, 486, 487\r\n" );
document.write( "488, 489, 490, 491, 492, 493, 495, 496, 497, 498, 499\r\n" );
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document.write( "Edwin
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