document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=12351>Question 12351</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I am having trouble figuring out how to use the identity property of 1 (how it works) on various problems. For instance here are two:<BR>\n" );
document.write( " Leon left a 15 percent tip for a meal, the total cost of the meal, including tip, was $41.40. What was the cost of the meal before tip? <BR>\n" );
document.write( "(In this problem we divide 41.40 by 1.15, how do we know we have to add 1 to the .15)<BR>\n" );
document.write( " Here's where I'm confused, between these two problems.\r<BR>\n" );
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document.write( " credit cards: The balance in Will's Mastercard account grew 2 percent, to $870 in one month. What was his balance at the beginning of the month?  <BR>\n" );
document.write( "(somehow we use I think .98 to this problem) how do we know we have to subtract .02 from 1)<BR>\n" );
document.write( " Please help me, in figuring why we subtract or add 1. How do we know which operation to use and how it works.<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 #6278 by </B><A HREF=/tutors/aboutme.mpl?userid=rapaljer><B>rapaljer(4671)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rapaljer><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=rapaljer><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=6278\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The 1 comes from 100%.  In your first problem, you said that the TOTAL bill, including the tip was $41.40.  This means that you have the cost of the meal, which is 100% of the meal PLUS 15% of the meal for the TIP.  That would be 115%.\r<BR>\n" );
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document.write( "Another way of looking at this is to say\r<BR>\n" );
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document.write( "Let x = cost of the meal.<BR>\n" );
document.write( ".15x = amount of the tip (since it is 15% of the meal cost)\r<BR>\n" );
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document.write( "The equation is based upon the fact that the total is<BR>\n" );
document.write( " x + .15x = 41.40\r<BR>\n" );
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document.write( "Do you see that the x in this equation represents 1x?  That's where the 1 comes from!!\r<BR>\n" );
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document.write( "In the case of a DISCOUNT, you would be subtracting the discount from 100% instead of adding it.  This is apparently how you came up with the 98% in your second illustration.  However, take another look at that.  I think your second illustration should ALSO be an add-on, since it began with x at the beginning of the month, and then it grew 2% to end up with $870.  I think that should be the same situtation as when you added the tip to end up with a total amount.  \r<BR>\n" );
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document.write( "R^2 at SCC </SPAN>\n" );
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