document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=496708>Question 496708</A>: <I><SPAN STYLE=\"word-break: break-all;\"> If the cost of a cell phone has decreased 400% during the past 10 years, does that correspond to a cost decrease of four times? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #336550 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=336550\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> i'm not sure you can say that.<BR>\n" );
document.write( "here's why:\r<BR>\n" );
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document.write( "suppose the cost was $500 per month 10 years ago.<BR>\n" );
document.write( "suppose the cost is now $100 per month.<BR>\n" );
document.write( "the cost has decreased by the following formula:<BR>\n" );
document.write( "$500 - x*$500 = $100<BR>\n" );
document.write( "add x*$500 to both sides of this equation and subtract $100 from both sides of this equation and you get:<BR>\n" );
document.write( "$500 - $100 = x*$500<BR>\n" );
document.write( "combine like terms to get:<BR>\n" );
document.write( "$400 = x*$500<BR>\n" );
document.write( "divide both sides of this equation by $500 to get:<BR>\n" );
document.write( "$400 / $500 = x which results in:<BR>\n" );
document.write( "x = 4/5 which is equal to 80%.\r<BR>\n" );
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document.write( "the original formula of:<BR>\n" );
document.write( "$500 - x*$500 = $100 becomes:<BR>\n" );
document.write( "$500 - .8*$500 = $100 which becomes:<BR>\n" );
document.write( "$500 - $400 = $100 which becomes:<BR>\n" );
document.write( "$100 = $100 which is true, confirming the value of x = .8 as good.\r<BR>\n" );
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document.write( "if you are looking at an increase in price, then the percentage figure can go higher than 100%.\r<BR>\n" );
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document.write( "]if you are looking at a decrease in price, then the percentage figure has to be less than 100%, otherwise the cost goes to 0 or below which is not good for business.\r<BR>\n" );
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document.write( "if you say that the previous price was 400% more than the current price, then you are talking about something entirely different.\r<BR>\n" );
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document.write( "now the formula becomes:\r<BR>\n" );
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document.write( "p = c + 4c which results:<BR>\n" );
document.write( "p = 5c\r<BR>\n" );
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document.write( "this says that the previous price was 5 times the current price.<BR>\n" );
document.write( "let's see if this works.\r<BR>\n" );
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document.write( "assume the current price is $100.<BR>\n" );
document.write( "if you say the previous price was $400 more than that, then the previous price was equal to $500.<BR>\n" );
document.write( "that equates to a price that is 5 times the current price.\r<BR>\n" );
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document.write( "the numbers are very tricky to work with, so you have to be careful how you express what you are trying to say.\r<BR>\n" );
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document.write( "you can say that the previous price is 400% higher than the current price, but you can't say that the current price is 400% lower than the previous price.\r<BR>\n" );
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document.write( "that's my thinking.<BR>\n" );
document.write( "i think i know what you meant, but it is technically wrong to express it the way that you did.\r<BR>\n" );
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document.write( "you can add more than 100% of the previous price and get a valid answer.<BR>\n" );
document.write( "you can't subtract more than 100% of the previous price and get a valid answer.<BR>\n" );
document.write( "the answer will be negative which you do not want to do unless you are paying people to take the product off your hands.\r<BR>\n" );
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document.write( " </SPAN>\n" );
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