Question 1205221
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As the problem is presented, there is no way to know what a is equal to.  By the definition of mod, a can be any number that differs from -25 by an integer multiple of 7.<br>
The usual intent of a problem like this is to have the answer equal to a non-negative number less than 7.<br>
So a typical correct presentation of the problem, allowing a single answer, would be something like this:<br>
"Solve: a ≡ -25 (mod 7) (0 <= a < 7)"<br>