document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1163146>Question 1163146</A>: <I><SPAN STYLE=\"word-break: break-all;\"> (a). john invested 4000 for a year, part at 7% per annum and part at 9% per annum. the interest on the investment is 300. how much did john invest at each rate?\r<BR>\n" );
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document.write( "(b). if 400 is deposited at a bank at 10% per annum compounded quarterly, how long will it take the deposit to double in value?\r<BR>\n" );
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document.write( "(c). a bowl collect 1.67cm height of water in its first week in a dewdrop. each week the height of the water increases by 4% more than it did the week before. by how much does it increase in nine weeks, including the first week?\r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #787128 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=787128\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "One question per post -- it is the clear rule of the post.  Re-post the other two problems separately.<br><BR>\n" );
document.write( "For a standard algebraic solution to the problem, the setup would be something like this:<br><BR>\n" );
document.write( "x amount at 7%, plus (4000-x) amount at 9%, equals 300<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=.07%28x%29%2B.09%284000-x%29+=+300 ALIGN=MIDDLE  ALT=\".07%28x%29%2B.09%284000-x%29+=+300\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "I leave it to you to finish solving the problem by that method.<br><BR>\n" );
document.write( "Here is a quick and easy method for solving a \"mixture\" problem like this if a formal algebraic solution is not required.<br><BR>\n" );
document.write( "(1) All $4000 invested at 7% would yield $280 interest; all at 9% would yield $360 interest.<BR>\n" );
document.write( "(2) The actual interest amount, $300, is 20/80 = 1/4 of the way from $280 to $360; therefore, 1/4 of the total was invested at the higher rate.<br><BR>\n" );
document.write( "ANSWER: 1/4 of $4000, or $1000, at 9%; the other $3000 at 7%.<br><BR>\n" );
document.write( "CHECK: .09(1000)+.07(3000) = 90+210 = 300<br><BR>\n" );
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