document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1207614>Question 1207614</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Hi<BR>\n" );
document.write( "A group of girls had an average height of 155cm.3 more girls joined the group and the average height became 157cm. If the 3 girls had the same height of 163cm each, how many girls were there at first. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #845591 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13203)</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=845591\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "The response from tutor @ikleyn shows a standard formal solution using the definition of average.<br><BR>\n" );
document.write( "When the problem is about averages and the numbers are very close together, a quick informal solution can be obtained by comparing the individual numbers to the average.<br><BR>\n" );
document.write( "In this problem, the 3 girls who joined the group each had a height of 163cm, which is 6cm above the new average of 157cm.  That makes a total of 3*6cm = 18cm over the new average.<br><BR>\n" );
document.write( "That means the heights of the original group of girls must be a total of 18cm under that new average.  Since the average height of the girls in the original group was 2cm under the new average, the number of girls in the original group was 18/2 = 9.<br><BR>\n" );
document.write( "ANSWER: 9<br><BR>\n" );
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