Two commonly used strategies for effective problem-solving are :

Correct Option: Heuristics and algorithms

Explanation:
Problem-solving is a cognitive process that involves finding solutions to difficult or complex issues. In psychology and computer science, two fundamental and commonly used strategies for solving problems are algorithms and heuristics.

1. Algorithms:
An algorithm is a step-by-step, defined procedure or formula that guarantees a correct solution if followed correctly. For instance, following a mathematical formula or a recipe is an algorithmic approach. While algorithms ensure accuracy, they can sometimes be slow and time-consuming.

2. Heuristics:
A heuristic is a mental shortcut or "rule of thumb" strategy that allows people to solve problems and make judgments quickly and efficiently. While heuristics save time and cognitive effort, unlike algorithms, they do not guarantee an accurate solution every time. Examples include trial and error, working backward, or using analogies.

Analysis of Other Options:
• Functional Fixedness: This is a cognitive bias that limits a person to using an object only in the way it is traditionally used. It acts as an obstacle to problem-solving, not a strategy.
• Response Set: This refers to a tendency to respond to questions or problems in a particular rigid way based on past experiences. Like functional fixedness, it hinders effective problem-solving rather than helping it.

Therefore, the two effective strategies used for problem-solving are heuristics and algorithms.