Barriers to Effective Problem Solving – MCAT Psychology | MedSchoolCoach

Barriers to Effective Problem Solving

MCAT Psychology - Chapter 2- Section 4 - Cognition - Intelligence & Problem-Solving
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Sample MCAT Question - Barriers to Effective Problem Solving

Which barrier to effective problem solving involves thinking that it is necessary to use all information provided to solve a problem?

a) Irrelevant Information

b) Functional Fixedness

c) Mental Set

d) Unnecessary Constraints

A is correct. The irrelevant information barrier to effective problem solving is the false notion that all information included with the problem is needed to solve the problem. Answer choice B is incorrect because functional fixedness is the tendency to perceive an object only in terms of its most common use. Answer choice C is incorrect because mental set occurs when people continually try to use a problem solving strategy that worked in the past, but may not necessarily be the correct method for the current problem. Answer choice D is incorrect because unnecessary constraints are when individuals assume there are rules that do not exist.

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Barriers to Effective Problem Solving for the MCAT

In the MCAT post, we explore four barriers to effective problem solving that are important to know for the Psychological, Social, and Biological Foundations of Behavior section of the MCAT. These four barriers are irrelevant information, functional fixedness, mental set, and unnecessary constraints.

Irrelevant Information

Irrelevant information is information included in a problem that is not related to or required to solve the problem. Irrelevant information is an issue because people generally believe that they need to use all the information provided in a problem to solve it. However, this is often not the case. To solve problems efficiently, it is necessary to determine what information is relevant.


Consider the problem: 30% of residents in Boston have unlisted telephone numbers. If you randomly select 150 names from the Boston telephone directory, how many of these people would you expect to have unlisted phone numbers? In this problem, the information provided is that 30% of residents have unlisted phone numbers, and 150 names are selected from the Boston telephone book. It can be tempting to think that the answer is just 30% of 150 people (45 people). However, this is not correct. The answer to this problem is actually zero because names taken from a telephone directory must have listed numbers. The 30% is a distractor in the problem and is not required to answer the question.

Functional Fixedness

Functional fixedness is the tendency to perceive objects only in terms of their most common uses. For example, in the String Problem depicted in Figure 1, two strings hang from a ceiling and need to be tied together. However, they are too far apart to allow a person to grab one and walk to the other. On the table is a pair of pliers. Most people can’t determine how to utilize the pliers to tie the two strings together because they think of the pliers as a tool to hold, bend, or compress objects.

The String Problem is an example of arrangement problem solving - MCAT Psychology
Figure 1: The String Problem

However, in the solution depicted in Figure 2, it can be seen that there are other ways to use pliers. The pliers can be connected to the string to make a pendulum and swung back and forth to allow someone holding one string to grab the other. By surpassing functional fixedness and being able to utilize objects in less common ways, problem-solving can be made easier.

The solution to the string problem as an example of arrangement problem solving for the MCAT
Figure 2: The String Problem's Solution

Mental Set

A mental set is the collection of problem-solving strategies that have worked for a person in the past. Take the Water Jar Problem as an example, where there are three empty water jars that can hold different volumes of fluids. Jar A can hold 37 cups of water, Jar B can hold 12 cups of water, and Jar C can hold five cups of water. The problem’s task involves filling and emptying the jars as many times as necessary to measure out 10 cups of water. The solution is to fill up Jar A with 37 cups of water. This is poured into Jar B, which removes 12 cups of water and leaves 25 cups of water in Jar A. Jar A is then poured into Jar C to remove five cups of water. This is done three times to remove 15 cups of water, leaving 10 cups of water in Jar A.


In trial two of the Water Jar Problem, Jar A can hold 43 cups of water, Jar B can hold nine cups of water, and Jar C can hold four cups of water. The goal is to measure out 22 cups of water. When presented with this problem, most people want to try the same solution that worked for trial one of the problems, allowing them to solve trial two faster. If Jar A is filled with 43 cups of water and poured into Jar B, nine cups of water will be removed, leaving 34 cups in Jar A. If Jar A is poured into Jar C three times, it will get rid of 12 total cups of water, resulting in 22 cups in Jar A.


Trial three of this problem is solved in the same way, and people solve trial three even quicker than the first two trials. Jar A holds 24 cups of water, Jar B holds four cups of water, and Jar C holds three cups of water. The goal is to measure out 11 cups of water. Jar A is filled with 24 cups of water and poured into Jar B to get rid of four cups of water. The remaining 20 cups of water in Jar A is poured into Jar C three times to get rid of nine total cups of water, resulting in the final goal of 11 cups of water.


In trial four of this problem, Jar A can hold 35 cups of water, Jar B can hold 13 cups of water, and Jar C four cups of water with the final goal of having nine cups of water. This is the easiest of the trials. However, after solving the first three trials, most people have a long, difficult time solving this one. This is because they attempt to solve it with the same strategy that worked for the last three trials, filling Jar A with 35 cups of water, pouring it into Jar B to yield 22 cups of water, and then pouring it into Jar C three times. However, this leaves Jar A with 10 cups of water, which is not the goal volume. The answer is simple and involves filling Jar B with 13 cups of water and pouring four cups out into Jar C to end with nine cups of water. Despite this being the simplest trial, mental set causes many to struggle to solve it.

Unnecessary Constraints

An unnecessary constraint is another barrier to effective problem solving and occurs when individuals assume that there are rules that don’t actually exist. For example, in the problem depicted in Figure 1, nine circles need to be connected using four lines. The unnecessary constraint that most people believe is that there is a barrier around the circles that can’t be crossed. With this unnecessary constraint, drawing four lines to connect the nine circles is impossible. However, without this unnecessary constraint, there are several possible solutions, two of which are depicted, demonstrating how problem-solving can be made easier by removing unnecessary constraints.

Figure 3: Problem Connecting Nine Points with Four Lines

To surpass barriers to effective problem solving, such as mental set and unnecessary constraints, it is necessary to think outside of the box and not be restricted to past strategies or constraints that don’t actually exist.

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