Chun and Devi started jogging from the same place in opposite directions along a straight path. They jogged for 40 minutes. At the end of the jog, they were 7 km apart. Chun's average speed was 6 km/h.
What was Devi's average speed?
6 x 40/60 = 4
7 - 4 = 3
3 x 60/40 = 4.5 km/h or 3/4 x 6 = 4.5 km/h
Alternative method
----------------------
7 ÷ 40/60 = 7 x 60/40 = 10.5 Combined speed
10.5 - 6 = 4.5 km/h
Subscribe to:
Post Comments (Atom)
As appeared in PSLE 2010 exam:
ReplyDeleteChun and Devi started jogging from the same place in opposite directions along a straight path. They jogged for 40 minutes. At the end of the jog, they were 7 km apart. Chun's average speed was 6 km/h.
What was Devi's average speed?
I don't get it. Why do you take "7-4=3"?
ReplyDeleteChun jogged at 6 km/h for 40 min, so the distance he covered was 4 km.
ReplyDeleteSince, they were 7 km apart, Devi jogged 7 - 4 = 3 km.
Sorry but i still do not get it.
ReplyDelete