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 Maha Bodhi 2010 Maths Prelim question - need help
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By: linjimt (offline)  Sunday, September 09 2012 @ 08:29 AM CDT (Read 823 times)  
linjimt

Hi, need explaination on how to solve this type of problem.

Q15.
If Mr Tiong drove at 60km/h, he would reach Town V at 1pm.
If he had driven at 80km/h, he would reach Town V at 12:30pm.
One day, Mr Tiong decided to drive at 100km/h to Town V.
How long did he take to reach Town V?

(1) 60 mins
(2) 72 mins
(3) 90 mins
(4) 96 mins.

Ans: (2).

Please explain how to derive the answer.

Thanks

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By: echeewh (offline)  Monday, September 10 2012 @ 08:33 PM CDT  
echeewh

Hi there,

Following pls find my worked solution:

Since Distance travelled is common (constant), the Speed ratio is inverse (reverse) of the Time ratio

S(1) : S(2)
60 : 80
3 : 4

T(1) : T(2)
4 : 3

4u - 3u --> (1/2) hr
1u --> (1/2) hr
T(2) = 3u --> 3 x (1/2) = (3/2) hr

D = S X T = S(2) X T(2) = 80 x (3/2) = 120 km

At S(3) = 100 km/h, T(3) = D ÷ S = 120 ÷ 100

= 1.2 hr = 72 mins

======================

Trust this helps.

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

Cheers,
Edward

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