Anyone have a formula for...

...calculating the decrease in water temp by adding grain?  I know BeerSmith will do all of the calculating for us, but I want to know the math behind it.  For example, if you know where your strike water will stabilize itself and your equipment when it's in the mash tun, what is the math that will calculate the additional temperature drop by adding the grain?  Something along the lines of "X amount of water at Y temp in a 10 lb mash tun with specific heat of 0.30 will be reduced to Z degrees by adding A lbs of grain."

From How to Brew (http://www.howtobrew.com/section3/chapter16-3.html):

Initial Infusion Equation:
Strike Water Temperature Tw = (.2/r)(T2 - T1) + T2

Mash Infusion Equation:
Wa = (T2 - T1)(.2G + Wm)/(Tw - T2)

r = The ratio of water to grain in quarts per pound.
Wa = The amount of boiling water added (in quarts).
Wm = The total amount of water in the mash (in quarts).
T1 = The initial temperature (¡F) of the mash.
T2 = The target temperature (¡F) of the mash.
Tw = The actual temperature (¡F) of the infusion water.
G = The amount of grain in the mash (in pounds).

One of my beercalc tools does this.  It is also in my aging android app.  I always miss my mash temp because I ballpark everything.  So, I created a tool to help me fix things.  Look at the bottom tool.  http://jomebrew.doesntexist.com/beercalc.htm

Thanks guys!  Dusted off the algebra skills and got what I needed from the equations.