Welcome, Iva. Thinking critically is no easy task, and there are plenty of resources out there to help you along. What anyone needs to do is develop some strategies for inculcating a set of skills, because critical thinking is a skill, and it is somewhat independent of IQ. There are also impediments to critical thought such as bias, deception, fallacy, illusion, and confabulation. The first step to improving critical thinking is read the WP articles above, and then moving on.
Also know, you are not alone. See related SE Posts:
How can I develop my critical thinking skills?
What is insight and can we develop it?
Rigorous, modern introductions to informal reasoning and critical thinking?
Having spent much time in conversation with Mensans, I can tell you that critical thinking is a skill that you'll find more among philosophers and mathematicians and engineers generally, because to some extent, critical thought is a product of an attitude more than a capacity. According to the American Bar Association, the best thinkers are:
1) Physics/math majors, with an average LSAT of 160.
2 and 3) Tied for second place, economics majors and philosophy/theology majors, with an average LSAT of 157.4.
4) International relations majors, with an average LSAT of 156.5.
5) Engineering majors, with an average LSAT of 156.2.
Of these majors, physicists, mathematicians, economists, and engineers are all students of an extensive amount of mathematics and logic, and philosophers receive formal training in logic, so it's a good bet that improving your logical and mathematical skills will help. In fact, at the university level, mathematics is essentially an exercise in logic. Majors in international relations, theologians, and philosophers are all engaged in practices which are highly logic-oriented.
It is not unreasonable to presume, then that math and philosophy are two excellent ways to improve logical skills and critical thinking ability, and it is an ability that can be improved. How? Studying and interacting with others, like you have done here.
As for your sample question, right away, a philosophy major would know that this problem is a logical problem referring to induction, deduction, and abduction, all forms of inference which is a skill used in argumentation. Once a student explores this topic, suddenly she is confronted with questions like what is meaning? How do syntax and semantics relate? What is truth? What is there really? How do I know that what I believe is true? (The last two questions are very important in critical thinking and are related to ontology and epistemology.)
In fact, your logic class is typical fare for philosophers:
Which of the following combinations are true?
1. it follows deductively that all ravens are black or the sky is blue
2. It follows deductively that all ravens are black and the grass is green
3. It follows deductively that all ravens are black
4. It can never constitute the premise set of a sound argument
A. 1, 3
B. 2, 3
C. Only 3
D. Only 4
This question is pulled from the musing of Carl Hempel and is known as the Raven Paradox, and presumes you have knowledge of deduction and propositional logic including the knowledge of modus ponens and logical conjunction. In fact, your problem can be seen as:
If P then Q, and P
So which of the following is true?
1. P or R
2. P and S
Therefore having a high IQ might help a thinker to intuit the rules, but for most, this is a matter of learning.
For anyone who is struggling with critical thinking and aspires to improve, it is often a question of persistence and education. Unless one has dyscalculia, IQ is most likely to determine the effort and speed one can acquire critical thinking skills, not determine if one can.
The journey of a thousand miles begins with a single step. - Lao Tzu