John D. Runkle School » Math http://www.runkle.org Brookline Public Schools Sat, 04 Feb 2012 04:38:14 +0000 en hourly 1 http://wordpress.org/?v=3.3.1 Runkle Math and Science Night – Friday May 20, 2011 http://www.runkle.org/2011/05/18/runkle-math-and-science-night-this-friday-may-20-2011/ http://www.runkle.org/2011/05/18/runkle-math-and-science-night-this-friday-may-20-2011/#comments Wed, 18 May 2011 20:46:58 +0000 The PTO http://www.runkle.org/?p=2955

]]> http://www.runkle.org/2011/05/18/runkle-math-and-science-night-this-friday-may-20-2011/feed/ 0 Math Problem of the Week: Tom & Bill http://www.runkle.org/2011/02/13/math-problem-of-the-week-tom-bill/ http://www.runkle.org/2011/02/13/math-problem-of-the-week-tom-bill/#comments Mon, 14 Feb 2011 00:42:05 +0000 Runkle News Editor http://beta.runkle.org/?p=2268 Tom is standing in a hole that is 4 feet deep. Bill asks him how much deeper he is going to dig the hole. Tom replies that he will dig 4 feet 2 inches deeper and that the top of his head will then be the same distance below ground level that it is now above ground level. How tall is Tom?

]]> http://www.runkle.org/2011/02/13/math-problem-of-the-week-tom-bill/feed/ 0 Math Problem of the Week: Investments http://www.runkle.org/2011/02/07/math-problem-of-the-week-investments/ http://www.runkle.org/2011/02/07/math-problem-of-the-week-investments/#comments Tue, 08 Feb 2011 00:51:53 +0000 Runkle News Editor http://beta.runkle.org/?p=2272 A man has $10,000 to invest. He invests $4,000 at 5 percent and $3,500 at 4 percent. To have a yearly income of $500 from the investment, at what rate must he invest the remainder of the money?

Solution

The man wants to earn $500 in interest each year. Investing $4000 at 5 percent yields yearly interest of 0.05 x $4000, or $200; whereas $3500 invested at 4 percent yields 0.04 x $3500, or $140; so the remaining $2500 needs to be invested at a rate that yields interest of $160 per year (to have a total interest of $500 each year). If r is the annual percentage rate for the $2500, then


So the man needs to invest the remaining $2500 at 6.4 percent or higher to guarantee an interest income of at least $500 a year.

— Mr. Lass

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