document.write( "Question 1011892: What is the 50th number in the pattern 7,9,11,13,15,...? \n" ); document.write( "
Algebra.Com's Answer #627701 by AnlytcPhil(1806)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "7,9,11,13,15,...?\r\n" );
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document.write( "I'll show you several ways:\r\n" );
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document.write( "Here's the crude way.  Write them out:\r\n" );
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document.write( " 7,  9, 11, 13, 15, 17, 19, 21, 23, 25,\r\n" );
document.write( "27, 29, 31, 33, 35, 37, 39, 41, 43, 45,\r\n" );
document.write( "47, 49, 51, 53, 55, 57, 59, 61, 63, 65,\r\n" );
document.write( "67, 69, 71, 73, 75, 77, 79, 81, 83, 85,\r\n" );
document.write( "87, 89, 91, 93, 95, 97, 99,101,103,105.\r\n" );
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document.write( "So we know the answer is 105.\r\n" );
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document.write( "Or we can do it another way:\r\n" );
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document.write( "7,9,11,13,15,...?\r\n" );
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document.write( "Subtract 5 from them all to get them down to\r\n" );
document.write( "a list of the even numbers:\r\n" );
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document.write( "2,4,6,8,10,,...?\r\n" );
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document.write( "Divide them all by 2\r\n" );
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document.write( "1,2,3,4,5,...?\r\n" );
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document.write( "Now we know the 50th term of that is 50. So we\r\n" );
document.write( "can put 50 for the question mark there:\r\n" );
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document.write( "1,2,3,4,5,...,50\r\n" );
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document.write( "So we undo what we did to them in reverse order, \r\n" );
document.write( "and see what happens to the 50.\r\n" );
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document.write( "The last thing we did was to divide by 2,\r\n" );
document.write( "so we undo that division by multiplying them all by 2:\r\n" );
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document.write( "2,4,6,8,10,...,100\r\n" );
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document.write( "Before that we subtracted 5 to get them down to the \r\n" );
document.write( "even numbers, so we undo that by adding 5 to them all:\r\n" );
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document.write( "7,9,11,13,15,...105 \r\n" );
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document.write( "So again, we see, it's 105.\r\n" );
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document.write( "Here's another way \r\n" );
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document.write( "The first term is a1\r\n" );
document.write( "To get the 2nd term, we add the common difference d 1 time  \r\n" );
document.write( "to the 1st term a1. a2 = a1 + (1)d\r\n" );
document.write( "To get the 3rd term, we add the common difference d 2 times \r\n" );
document.write( "to the 1st term a1. a3 = a1 + (2)d\r\n" );
document.write( "To get the 4th term, we add the common difference d 3 times \r\n" );
document.write( "to the 1st term a1. a4 = a1 + (3)d\r\n" );
document.write( "...\r\n" );
document.write( "To get the nth term, we add the common difference d n-1 times \r\n" );
document.write( "to the 1st term a1. an = a1 + (n-1)d\r\n" );
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document.write( "an = a1 + (n-1)d\r\n" );
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document.write( "That's where the formula comes from.\r\n" );
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document.write( "In your problem,\r\n" );
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document.write( "7,9,11,13,15,...?\r\n" );
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document.write( "to get the 50th term, add common difference 2, 49 times to the 1st term\r\n" );
document.write( "a1 = 7. \r\n" );
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document.write( "an = a1 + (n-1)d\r\n" );
document.write( "a50 = 7 + (50-1)2\r\n" );
document.write( "a50 = 7 + (49)2\r\n" );
document.write( "a50 = 7 + 98\r\n" );
document.write( "a50 = 105\r\n" );
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document.write( "Edwin
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