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 By: shirley wee (offline)  Sunday, June 16 2013 @ 02:33 AM CDT (Read 809 times)
shirley wee

Hi everybody! I'm stuck with this maths question. May you help me? Please show your working clearly.

Q1. Kelly and Tom started walking from the same starting point but in the opposite directions along a straight path. Kelly's average speed was 4km/h faster than Tom's. After walking fo 3 hours, they were 40km apart. What was Kelly's average speed?

Chatty

Registered: 02/28/12
Posts: 68

 By: jo sarah (offline)  Wednesday, June 19 2013 @ 07:28 AM CDT
jo sarah

Q1. Kelly and Tom started walking from the same starting point but in the opposite directions along a straight path. Kelly's average speed was 4km/h faster than Tom's. After walking fo 3 hours, they were 40km apart. What was Kelly's average speed?

Solution:

If Kelly's speed is 4 km/h faster than Tom's,
then after 3 hours, she would have travelled 4 km/h x 3 h = 12 km more than Tom

If they are 40 km apart, then sum of distances travelled by both = 40 km (because they went in opposite directions)

Therefore, Kelly's distance is (40 + 12)/2 km = 26 km
And, so her average speed = 26 km/3 h = 8 2/3 km/h

check:
Tom's distance = (40 - 26) km = 14 km
and his speed = 14 km/3 h = 4 2/3 km/h, which is 4 km/h slower than Kelly's

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Registered: 03/20/12
Posts: 111

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