Just 2.5 examples:
1. "Polish" notation or "Tape calculator".
Try to start with 78 (for diamond) and press corresponding symbols on the
calculator ("-" when you hear/read "minus" and "=" when you hear/read
"equals", etc..).
In this (calculator) context "equals" can be interpreted as "perform
calculation" and the teacher, possibly, was asking kids to restore all
intermediate results in the sequence of calculations which led to 211 (like
in, "kids, let's restore what was on the tape if cashier presses '=' after
every arithmetic operation").
2. Programming languages.
I wonder how many of you saw expressions like
i = i + 1
in any program written in any more or less popular programming language
(FORTRAN, ALGOL, PL/1, SAS, C, Basic, etc)
In this context "equals" means "assign", but nobody (except N. Wirth,
inventor of Pascal) bothered to introduce a special symbol for it.
2.5 Set theory.
This example is rather for the "+" and "*" ambiguity.
It is normal to see expressions like
A = A + A
or A = A * A
in the set theory, Boolean logic or even theory of probability papers,
because that is how "union" and "intersection" are represented sometimes.
Conclusion.
Forget natural languages, even in exact sciences, symbols are subjects to
interpretation depending on the context and naming conventions: I would
leave poor 3rd Grade teacher alone..
Alex
P.S. And don't even mention "Annuity symbols..."
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