When the situation is described, if the description says that one amount 'IS' the other amount, or 'is equal to' the other amount, or 'is the same as' the other amount, that's your cue to use an equation.
But if you hear any of the phrases on this list, then it's asking for an inequality:
-- ' more than ' -- ' bigger than ' -- ' less than ' -- ' smaller than ' -- ' not more than ' -- ' not less than ' -- ' at least ' -- ' the most '