How to find the angle of clock hands - ISEE Upper Level Quantitative Reasoning

Card 1 of 20

0
Didn't Know
Knew It
0
1 of 2019 left
Question

At which of the following times on a clock is the smaller angle created by the minute hand and hour hand NOT less than ?

Tap to reveal answer

Answer

In this problem, you are working with the shape of a clock. A clock is in the shape of a circle, which has total. You are looking for the time for which the smaller angle created by the minute and hour hands is NOT less than - in other words, the time must create an angle greater than .

First, it's helpful to recognize at what times a right angle () exists. This would be 3:00 and 9:00. It's also useful to recognize that times such as 3:30 and 9:30 will be slightly under - the hour hand moves just past the 3 and 9 on a clock at these times to create this effect. You can draw a clock out to show these angles.

The three times that do create an angle less than , and thus are incorrect, are 2:00, 4:30, and 11:00.

2:00 has the minute hand straight up on the 12 and the hour hand straight at the 2, making it less than the angle created by 3:00.

4:30 has the hour hand in between the 4 and 5 and the minute hand on the 6, making it less than the angle created by 3:30.

11:00 has the minute hand straight up on the 12 and the hour hand straight at the 11, making it less than the angle created by 9:00.

1:30 is the angle that is NOT less than . The hour hand is in between the 1 and 2, and the minute hand is straight down on the 6. This angle is larger than a perfect right angle of . Therefore, 1:30 is the correct answer.

← Didn't Know|Knew It →