When we assign the wrong function, it can cause problems. For the Duncker candle problem discussed in the text there was a box of tacks, a candle, a hammer and a book of matches. For well defined problems, the heuristic approach provides a guaranteed solution. A heuristic is sometimes also called a 'rule of thumb'. Algorithms have a probabilistic solution.
Algorithms are precise procedures for calculating a result from specific starting states.
So, in an magnitude estimation task, subjects are not given time to calculate the answer to, e.g., a math problem, but must very quickly make a guess. Sorry, not right. The eagle is a very well known bird, and we see its likeness in many public signs and national symbols, so it is very frequent and familiar. Sorry, not right. A turkey is easily recognizable and familiar, but not prototypical.