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
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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