The SAT Question Everyone Got Wrong

Summary by Krater

This video examines a notoriously flawed math question from the 1982 SAT, exploring the 'coin rotation paradox' to explain why the intuitive answer was wrong and how the college board ultimately rescored the test.

From the video

Answers: Why did every student get question 17 wrong on the 1982 SAT?

• SAT math question 17 error
• Coin rotation paradox
• Sidereal vs solar year
• Sidereal time in astronomy
• Gear rotation mechanics

What it concludes

• The 1982 SAT question 17 had no correct answer among the given options because the test writers themselves got it wrong.
• When a smaller circle rolls around an identical circle, it rotates twice rather than once, which is known as the coin rotation paradox.
• The total number of rotations of a circle rolling around another circle is the ratio of their circumferences plus one.
• Sidereal time, based on the stars rather than the sun, accounts for the extra rotation Earth makes in its orbit each year.
• The college board publicly admitted the error a few weeks later and rescored the test for all test takers.