Clock Hands PerpendicularDate: 10/15/2001 at 22:14:21 From: Carla Taylor Subject: Math What time of day is it when the hour hand is perpendicular to the minute hand and the minute hand points to the number 12? Date: 10/16/2001 at 13:21:32 From: Doctor Sarah Subject: Re: Math Hi Carla - thanks for writing to Dr. Math. Do you know what perpendicular means? Two lines that are perpendicular form a right angle of 90 degrees, or what looks like the corner of a square, when they meet. So let's draw a picture, starting with the minute hand. We know that the minute hand is pointing to the number 12: 12 11 ^ 1 | 10 | 2 | 9 o 3 8 4 7 5 6 Now we'll draw an hour hand perpendicular to the minute hand: 12 11 ^ 1 | 10 | 2 | 9 o------> 3 What time does this clock show? 8 4 7 5 6 But wait! There's another way to draw the hour hand perpendicular to the minute hand... 12 11 ^ 1 | 10 | 2 | 9 <------o 3 What time does this clock show? 8 4 7 5 6 Does this help? - Doctor Sarah, The Math Forum http://mathforum.org/dr.math/ Date: 10/16/2001 at 12:11:56 From: Doctor Achilles Subject: Re: Math Hi Carla, Thanks for writing to Dr. Math. The minute hand points to 12 every hour on the hour. In other words, at 1:00, 2:00, 3:00, 4:00, etc., 12 is straight up, so your question is which number is perpendicular to 12. If you look at a clock, you'll see that 3 and 9 are both perpendicular to 12, so there are two times of day that work: 3:00 and 9:00. Hope this helps. If you have other questions about this or other math topics, please write back. - Doctor Achilles, The Math Forum http://mathforum.org/dr.math/ |
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