20. At which time do the hands of an analog clock form an interior right angle?
Answer: C
The hands of an analog clock form an interior right angle at 9:00.
At 9:00, the hour hand is positioned at the 9 mark and the minute hand is at the 12 mark, creating a perfect right angle of 90 degrees between them.
A) 2:35
At 2:35, the minute hand is on the 7 mark, while the hour hand is slightly past the 2 mark. The angle between the two hands is not a right angle, as it measures greater than 90 degrees.
B) 3:15
At 3:15, the minute hand is on the 3 mark and the hour hand is a quarter of the way between the 3 and 4 marks. This configuration results in an angle that is less than 90 degrees, not a right angle.
C) 9:00
At 9:00, the hour hand is exactly on the 9, and the minute hand is on the 12, forming a right angle of 90 degrees. This is the only option where the hands of the clock create an exact right angle.
D) 6:00
At 6:00, the hour hand is at the 6 and the minute hand is at the 12, creating a straight line rather than a right angle. Therefore, this does not satisfy the condition of forming a right angle.
Conclusion
The correct answer is 9:00, where the hands of the clock create a perfect right angle. All other options either exceed or do not meet the criteria for forming a right angle, confirming that 9:00 is the only correct choice.