Saturday, March 27, 2010

Speed P6 2009 SA2 P2 Rulang Q11

11. Mr Lee left Town M and travelled towards Town N at an average speed of 80 km/h. An hour later, Mr Ong left Town M and travelled towards Town N at an average speed of 100 km/h. Mr Ong passed Town Q which was halfway between Town M and Town N 30 minutes earlier than Mr Lee. If Mr Ong reached Town N at 10 pm, at what time did Mr Lee leave Town M for Town N?


 
    M                                               Q                                               N
     !------------------------------------------------!------------------------------------------------!
     1 h                80 km/h             0.5h
L  [   ][        ][        ][        ][        ][ ]
O [        ][        ][        ][        ][       ][        ][        ][        ][        ][       ]  
                        100 km/h                                                            10 pm
                       
1 u -- > 80 x 1.5 = 120 km
10 u -- > 10 x 120 = 1200 km

1200 ÷ 10 = 12 h
       1 h                  12 h
  !----------!----------------------------!
9 am   10 am                          10 pm 

Mr Lee left Town M at 9 am.

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