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 Forum Index >  Test Paper Related >  Primary 6 Matters
 P6 Math Speed Question
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By: acelow (offline)  Saturday, September 14 2013 @ 01:19 AM CDT (Read 859 times)  
acelow

Alvin travelled from Town X to Town Y at an average speed of 72km/h. He travelled 7/12 of the journey at an average speed of 70km/h.After that, he decided to increase his speed to travel the remaining his speed to travel the remaining 450km to Town Y

(a) Find Alvin's speed in the last 450km of the journey
(b) If Kai Li started her journey from Town Y to Town X at the same time as Alvin at a constant speed of 90km/h, how far would she have travelled before she met Alvin?

Ans: (a): 75km/h
(b) 607.5km

Pls help again.
Thank you Smile

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By: echeewh (offline)  Sunday, September 15 2013 @ 01:26 AM CDT  
echeewh

Hey <acelow>,

Following is my worked solution:

(a)
(5/12)journey = 450 km
(12/12)journey = 450 × (12/5) = 1080 km

Total time taken = Total Distance / Average Speed (for whole journey)
= 1080 ÷ 72 = 15 hrs

(7/12)journey = 1080 - 450 = 630 km
time taken [(7/12)journey] = 630 ÷ 70 = 9 hrs

time taken [(5/12)journey] = 15 - 9 = 6 hrs

Average speed [(5/12)journey]
= 450 ÷ 6 = 75 km/h

(b)
Time taken to meetup = 1080 ÷ (70 + 90)
= 1080 ÷ 160
= 6.75 hrs

Dist travelled by K:
= 90 × 6.75
= 607.5 km

==========

Trust this helps.

Do let me know again if there's further clarification.

Cheers,
Edward

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