Making the leap from Pre-Calculus to Calculus

This question is targeted at teachers who taught both low and high level mathematics. I have a group of students that I'm currently teaching precalculus and they seem to be doing really well in all computational areas. For example, they can all do a problem like "Find the partial fraction decomposition of $$\frac{3x}{x^2-4}$$" or "Compute $$\lim\limits_{x\to\infty}\frac{x^3+2e^x}{3-e^x}$$". However, as soon as we hit abstract notions, they fall apart. We just reached Intermediate Value Theorem and they just can't seem to make the leap into abstraction. Consider a multiple choice question:

Let $$f(x)$$ be a continuous function and let $$f(1) = 3$$ and $$f(3)=11$$. Which of the below statements must be true?

1. $$f(x)$$ is increasing on the interval $$(1,3)$$
2. $$f(2)=7$$
3. $$f(x) = 5$$ for some value of $$x$$
4. $$f(x)$$ has a local maximum in the interval $$(1,3)$$

The majority of the students chose 1 and only a few chose the correct answer 3. We did 3 or 4 similar exercises and I explained each one (or so I thought). By the time we did a similar question #4, there was only a moderate improvement. Can someone suggest how to help students make a leap into the abstraction? How do you teach abstract concepts to students who have only encountered computational problems in their math careers?

• Ask them to draw a picture that supports the answer given. Jun 24 '21 at 8:38