SOLUTION: It is now past 3 o'clock in the afternoon. The minute hand 3 minutes from now will be directly opposite the hour hand 9 minutes ago. What time is it?

Algebra ->  Finance -> SOLUTION: It is now past 3 o'clock in the afternoon. The minute hand 3 minutes from now will be directly opposite the hour hand 9 minutes ago. What time is it?      Log On


   



Question 1092286: It is now past 3 o'clock in the afternoon. The minute hand 3 minutes from now will be directly opposite the hour hand 9 minutes ago. What time is it?
Answer by ikleyn(52814) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let the current time under the question be 3 hours and "t" minutes, where t is the real number, so t can be fraction of minutes and seconds.


The minute hand is at angular position  of  %28360%2F60%29%2At = 6t degrees, counting from its position "vertically up" at 3:00 pm.

     *** Minute hand makes its full revolution of  360 degrees in 60 minutes. ***


The hour hand at this moment is at the angular position  90+%2B+%281%2F12%29%2A%28360%2F60%29%2At degrees, counting from its position "vertically up" at noon.

     *** Hour hand has the angular velocity 12 times less than the minute hand: it is 12 times slower. ***


Three minutes from now the minute hand will be in position of  %28360%2F60%29%2At+%2B+%28360%2F60%29%2A3  degrees.


Nine minutes ago the hour hand was in position of  90+%2B+%281%2F12%29%2A%28360%2F60%29%2At+-+%281%2F12%29%2A%28360%2F60%29%2A9  degrees.


Therefore, the governing equation is 


%28360%2F60%29%2At+%2B+%28360%2F60%29%2A3 = 90+%2B+%281%2F12%29%2A%28360%2F60%29%2At+-+%281%2F12%29%2A%28360%2F60%29%2A9 + 180  degrees.


          The major part is done: the equation/the model is set up.

          The rest is just arithmetic. 


Simplify this equation

6t + 18 = 90+%2B+%281%2F12%29%2A6t+-+%281%2F12%29%2A6%2A9+%2B+180  ====>

6t+-+t%2F2 = 90+-+%289%2F2%29+%2B+180+-+18  ====>  %2811%2F2%29%2At = 2471%2F2  = 495%2F2 ====>

t = 495%2F11 = 45 minutes

Answer.  The current time is  3:45 pm.


             **************
             *** SOLVED ***
             **************