SOLUTION: 3.mr. kumar lives in the eastern part of the singapore. he visits his aged parents who lives 36 km away, evry weekends. he finds that if he increases the average speed of his vehic

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Question 388274: 3.mr. kumar lives in the eastern part of the singapore. he visits his aged parents who lives 36 km away, evry weekends. he finds that if he increases the average speed of his vehicle by 12 km/h.he could save 9 min of his travelling time. find the speed at which he travels before the increase in speed
Found 2 solutions by stanbon, josmiceli:
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
mr. kumar lives in the eastern part of the singapore. he visits his aged parents who lives 36 km away, every weekends.
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he finds that if he increases the average speed of his vehicle by 12 km/h.he could save 9 min of his traveling time.
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find the speed at which he travels before the increase in speed
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Current Round-Trip DATA:
distance = 72 km ; rate = x km/h ; time = 72/x hrs.
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Changed DATA:
distance = 72 km ; rate = (x+12) km/h ; time = 72/(x+12) hrs.
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Equation:
old time - new time = 9/60 hrs
(72/x) - (72/(x+12)) = 9/60 hrs
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Divide thru by 9:
8/x - 8/(x+12) = 1/60
60*8(x+12) - 60*8x = x(x+12)
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60*8*12 = x(x+12)
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x^2+12x-60*8*12 = 0
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Positive solution:
x = 70.13 km/h (current driving rate)
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Cheers,
Stan H.
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Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
Let = his time before he increases his speed.
Let = his rate before he increases his speed
given:
(1)
(2)
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(2)
Substituting from (1):

Multiply both sides by

Use quadratic formula

the other root is ignored since it is negative
His speed before the increase is 48 km/hr
Check answer:
(1)

(2)

OK