Simultaneous Equations
A Jones,
Leeds.
Your Computer, February 1982, page 74

As this program contains no Peeks or Pokes, it could run on many other machines
in addition to the 1K ZX-81 for which it was written. It solves simultaneous 
equations of a standard found in GCE O-level and CSE mathematics exam papers. 
Not only can it be used to do homework, but it can be used to solve general 
logic puzzles. For example:

 Fred buys three apples and two bananas which cost him 4p. Then George buys 
 seven apples and three bananas which cost him 11p. If X equals apples and Y 
 equals bananas, find how much one apple costs and how much one banana costs.
 3X + 2Y = 4
 7X + 3Y = 11

First the title is printed. Lines 20 to 130 are involved with the inputting of
the equations and lines 150 t0 170 print the two equations. Lines 180 to 190 
change variables B and C to negative numbers and then they are applied to the 
formula in line 200 and 210.

The lines 220 to 240 print the appropriate values of X and Y. The remainder of
the program then asks you whether you wish for another equation to be solved.

If we consider the Fred and George example two equations were:
  3X + 2Y = 4
  7X + 3Y = 11

The program first asks to input the X value. Here you would type 3 and Newline.
Then it instantly asks for the Y va1ue. You type 2 and a Newline. Then, when it
asks for the answer, type 4. It then continues to question you on the second 
equation. After this, the screen clears and the two equations are printed
followed by the two numbers that X and Y represent - the first is X.