Nowhere in the question does it say how many children Mrs. Johnson has, nor that all the muffins get eaten. Can we make an assumption about the total numbers? Yes. Are we thinking critically when we do so? No.
From a mathematical or critical thinking perspective, there are an infinite number of correct answers.
If you make assumptions you can get it down to three sets of correct answers. If you are the type of person who looks at this question and automatically makes those assumptions, you put on blinders. You have been properly trained so as to NOT think critically.
Congratulations and good luck in your cubicle career.
