
By: linjimt (offline) Sunday, September 09 2012 @ 08:29 AM CDT (Read 844 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

Newbie
Registered: 09/05/11 Posts: 4





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

Active Member
Registered: 04/21/11 Posts: 625



