Rashi uses the simple algebraic equations presented in the next
paragraph to infer currency equivalancies. The verses in question are
 Ex3825
And the silver of those who were counted of the congregation was a hundred (100) Kikar, and a thousand seven hundred and seventy five (1775) sacred shekels
 Ex3826
A bekah for every man, that is, half a sacred shekel, for every one who went to be counted, from twenty years old and upward, for six hundred and three thousand five hundred and fifty (603,550) men.
 Ex3013
This they shall give, every one who passes among those who are counted, half a sacred shekel a shekel is twenty gerahs; a half shekel shall be the offering of the Lord.
Rashis goals were to ascertain the relationship between the currencies mentioned:
the Kikar and Shekel. In performing the algebra below we will therefore
find it convenient to use abbreviation initials as follows:
 K will stand for Kikar
 S will stand for Shekel
 B will stand for the Beka.
In the derivation below we number ((1),(2),(3)) equations referred to. We indicate
verses as well as the equations derived from those verses. As can be seen one
Kikkar is 3000 shekel.
Equation (1) Ex3825 Total Silver Brought in = 100 K + 1775 S
Equation (2) Ex3826 Total Silver Donated = 603550 B
Equation (3) Ex3013,Ex3826 B = 1/2 S

By equations (1) and (2) 100 K + 1775 S = 603550 B
By equation (3) 100 K + 1775 S = 603550 1/2 S
By arithmetic 100 K + 1775 S = 301775 S
By subtraction 100K = 300000 S
By division 1 K = 3000 S
Rashi in addition to the Biblical commentary, also adds, as he does on rare occasions,
commentary on Rabbinic measures. Rashi introduces the following additional currency
equivalancies for Rabbinic currencies.
1 Kikar = 60 Maneh, known Rabbinic currency
Sacred Kikar = Double the ordinary Kikar
1 Sacred Kikar = 120 Maneh, combining the last 2 equations
1 Kikar = 3000 Shekel, from the last paragraph
120 Maneh = 3000 Shekel,combining the last 2 equations
1 Manen = 25 shekel, by division
Finally Rashi explains that 1 Maneh = 25 Selah his point being
that what the Bible calls a Shekel is called a Sela in Rabbinic currency.
This example is a peach of an example of the nonverse, algebraic, spreadsheet
method.
