SOLUTION: Mr Kumar lives in the eastern part of Singapore. He visits his aged parents, who lives 36km away, every weekend. He finds that if he increases the average speed of his vehicle by 1

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Question 522011: Mr Kumar lives in the eastern part of Singapore. He visits his aged parents, who lives 36km away, every weekend. He finds that if he increases the average speed of his vehicle by 12km/h, he could save 9 minutes of his travelling time. Find the speed at which he travels before the increase in speed.
Answer by lwsshak3(11628) About Me  (Show Source):
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Mr Kumar lives in the eastern part of Singapore. He visits his aged parents, who lives 36km away, every weekend. He finds that if he increases the average speed of his vehicle by 12km/h, he could save 9 minutes of his travelling time. Find the speed at which he travels before the increase in speed.
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let x= Mr Kumar's speed initially
x+12= Mr Kumar's increased speed
Travel time=distance/speed
9 minutes=9/60=.15 hr
36/x-36/(x+12)=.15
LCD:x(x+12)
36(x+12)-36x=.15x(x^2+12x)
36x+432-36x=.15x^2+1.8x
.15x^2+1.8x-432=0
let student solve for x by quadratic formula below:
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
..
x=48
or
x=-60 (reject)
ans:
Mr Kumar's initial speed was 48 km/hr