document.write( "Question 1153676: Select the option for \"?\" that continues the pattern in each question.
\n" ); document.write( "58
\n" ); document.write( "3, -6, 12, 4, 20, ?
\n" ); document.write( "13
\n" ); document.write( "14
\n" ); document.write( "6
\n" ); document.write( "16
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Algebra.Com's Answer #775940 by MathLover1(20850)\"\" \"About 
You can put this solution on YOUR website!
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\n" ); document.write( "\n" ); document.write( "These numbers are related in the following way, beginning with \"3\": \r
\n" ); document.write( "\n" ); document.write( "First, we subtract \"9\" to get \"-6\": \r
\n" ); document.write( "\n" ); document.write( "\"3+-+9=+-6\"\r
\n" ); document.write( "\n" ); document.write( " Next, we add \"18\": \r
\n" ); document.write( "\n" ); document.write( "\"-6+%2B+18=+12\"\r
\n" ); document.write( "\n" ); document.write( " To get from \"12\" to \"4\", we subtract \"8\": \r
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\n" ); document.write( "\n" ); document.write( "\"12+-+8+=+4\", and \r
\n" ); document.write( "\n" ); document.write( "to get from \"4\" to the final number of \"20\", we must add \"16\": \r
\n" ); document.write( "\n" ); document.write( "\"4+%2B+16=+20\"\r
\n" ); document.write( "\n" ); document.write( " We need to examine the numbers that we add/take away in the sequence to find a pattern so we can predict the next number.\r
\n" ); document.write( "\n" ); document.write( "So, let's look at the relationship between the numbers we added and subtracted to get from \"3\" to \"-6\", from \"-6+\"to \"12\", and so on. \r
\n" ); document.write( "\n" ); document.write( "First, we subtracted \"9\", then added \"18\", then subtracted \"8\", then added \"16\". \r
\n" ); document.write( "\n" ); document.write( "Think of ways in which the numbers \"9\", \"18\", \"8\", and \"16\" are related. \r
\n" ); document.write( "\n" ); document.write( "If I start with \"9\", I have to multiply by \"2\" to get \"18\": \r
\n" ); document.write( "\n" ); document.write( "\"9+%2A+2=+18\"\r
\n" ); document.write( "\n" ); document.write( " To get from the next number, \"8\", to the fourth in the sequence, \"16\", I must multiply by \"2\" again: \r
\n" ); document.write( "\n" ); document.write( "\"8+%2A+2=16\" \r
\n" ); document.write( "\n" ); document.write( "Now, we know the relationship between \"9\" and \"18\", and the relationship between \"8\" and \"16\". \r
\n" ); document.write( "\n" ); document.write( "We still need to figure out why the pattern moves from adding \"18\" to subtracting \"8\". To do this, I returned to my idea of multiplying by \"2\", which grouped our numbers as follows: \r
\n" ); document.write( "\n" ); document.write( "\"9\" was related to \"18\", and \"8\" was related to \"16\". \r
\n" ); document.write( "\n" ); document.write( " We can see that \"9-1=8\". \r
\n" ); document.write( "\n" ); document.write( " So, let's say \"9\" is \"\"x\".\" The relationship between the numbers in the original sequence can be summed up as follows: \r
\n" ); document.write( "\n" ); document.write( "First number in the sequence \"-x\", \"2x\", \"-+%28x-1%29\", \"+2%28x-1%29\". \r
\n" ); document.write( "\n" ); document.write( "Let's plug in \"3\" as the \"first\" number in the sequence and \"9\" as \"x\" to test our pattern: \r
\n" ); document.write( "\n" ); document.write( "\"3+-+9=+-6\"
\n" ); document.write( "\"-6+%2B+2%289%29=+-6+%2B+18=+12\"
\n" ); document.write( "\"12+-+%289-1%29=+12+-+8=+4\"
\n" ); document.write( "\"+4+%2B+2%289-1%29+=+4%2B+2%288%29+=+4+%2B+16=+20\"\r
\n" ); document.write( "\n" ); document.write( " If we put those answers in order, we have \"3\", \"-6\", \"12\", \"4\", \"20\": the original sequence! \r
\n" ); document.write( "\n" ); document.write( "Using the pattern we found in that equation, we can predict that the next number in the sequence would be related to \"20\" by subtracting \"%28x-2%29\", where \"x+\"still equals \"9\", since in order to get \"4\" after \"12\" we had to subtract \"%28x-1%29\" from \"12\". \r
\n" ); document.write( "\n" ); document.write( "So, \"20+-+%28x-2%29\" becomes \"20+-+%289-2%29+=+20+-+7=+13\". \r
\n" ); document.write( "\n" ); document.write( "so, answer is: \"13\"\r
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