A pass mark of 33 percent means a student must answer roughly one out of every three questions correctly.
The rule was introduced to give a fair chance during early standardized testing when many questions were difficult.
Schools continue to use it because it is easy to calculate and understand.
Some modern educators discuss changing the mark to match current teaching methods, but the historic number remains common.
Educators chose this percentage to ensure that even if a test was hard, a student could still demonstrate basic understanding and move forward.
Today, the same rule is often kept because it provides a simple and clear benchmark for teachers and students alike.
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