document.write( "Question 944285: Hello,
\n" ); document.write( "How can I find \"a%5B1%5D\" and d if
\n" ); document.write( "\"+a%5B4%5D=16+\" and \"+s%5B15%5D=420++\" ?\r
\n" ); document.write( "\n" ); document.write( "I am not sure which formula to use.
\n" ); document.write( "Thanks so much. \n" ); document.write( "
Algebra.Com's Answer #575738 by stanbon(75887)\"\" \"About 
You can put this solution on YOUR website!
a[4]=16 and s[15]=420
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\n" ); document.write( "Equations:
\n" ); document.write( "a(1) + 3d = 16
\n" ); document.write( "a(1) + 14d = 420
\n" ); document.write( "-----
\n" ); document.write( "Subtract and solve for \"d\"::
\n" ); document.write( "11d = 404
\n" ); document.write( "d = 404/11
\n" ); document.write( "-----
\n" ); document.write( "Solve for a(1)::
\n" ); document.write( "a(1) + 3(404/11) = 16
\n" ); document.write( "a(1) = 16 - 1212/11
\n" ); document.write( "a(1) = 176/11 - 1212/11
\n" ); document.write( "a(1) = -1036/11\r
\n" ); document.write( "\n" ); document.write( "==================
\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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