In terms of word-problem solving, any assertion or statement of fact translates into an equation. Since equations can be formed by stating that two expressions are equivalent, and the formation of expressions has been covered, the discussion of equations can be characterized by how equivalence can be stated.
Depending on the style of input, equations can be given in a few different ways:
Statements of fact are not the only kind of natural language that create equations... In Natural Language, non-trivial questions can produce equations (themselves "statements-of-fact") that must be solved to answer the question.
> How much less than e is Pi over two?
Let 'A' stand for "ANSWER"
(Find A)
Solving for A:
3.14159
2.71828 - A = -------
2
3.14159
- A = - 2.71828 + -------
2
3.14159
A (- 1) = - 2.71828 + -------
2
3.14159
A = 2.71828 - -------
2
A = 1.147485
1.147485 is THE ANSWER.
> There are how many times as many alphas as betas?
Let 'N' stand for "NUMBER"
(Find N)
Let 'A' stand for "ALPHAS"
Let 'B' stand for "BETAS"
So...
A
N = -
B
> How many unit cm longer than 6 unit inches is half a unit yard?
Let 'N' stand for "NUMBER"
(Find N)
Let 'C' stand for "CENTIMETER"
Let 'I' stand for "INCHES"
Let 'Y' stand for "YARD"
So...
6 N 1
- + - = ---
I C 2 Y
Regardless of their complexity or origin, the resulting equations are statements-of-fact about variables.