Read more:"Everyone is wise until he speaks."
- (Proverb)
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| 9. |
A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:
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| [A]. |
35.55 km/hr | [B]. |
36 km/hr | | [C]. |
71.11 km/hr | [D]. |
71 km/hr |
Answer: Option C
Explanation:
| Total time taken = |
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160 |
+ |
160 |
 hrs. |
= |
9 |
hrs. |
| 64 |
80 |
2 |
 Average speed = |
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320 x |
2 |
km/hr |
= 71.11 km/hr. |
| 9 |
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Nisha said:
(Mon, Jun 14, 2010 04:47:08 PM)
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| Can we use the formula for avg speed, ie: 2xy/(x+y) ?This formula gives a different answer. |
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S.Dineshkumar said:
(Wed, Jun 16, 2010 06:00:08 AM)
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Can you explain how 9/2 hrs came ...
Can you explain the question ones again? |
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Ranjith said:
(Sun, Jun 27, 2010 05:19:41 AM)
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| while using the formula for avg speed, as nisha said it gives a different answer.. |
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Sundar said:
(Sun, Jun 27, 2010 08:37:06 AM)
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Hi Nisha and Ranjith,
Average speed = 2xy/(x+y)
Where x = 64 km/hr and y = 80 km/hr.
Avg Speed = (2 x 64 x 80)/(64 + 80)
= 10240/144
= 71.111 km/hr
It is giving the correct answer only. Please make sure once again.
Hi Dinesh,
Your doubt is "How did 9/2 hrs come?".
1. The time taken for travelling first 160 km at 64 km/hr is = 160/64 = 2.5 hrs.
2. The time taken for travelling the next 160 km at 80 km/hr is = 160/80 = 2 hrs.
Therefore, total time taken (for 160 + 160 = 320 km) = 2.5 + 2 = 4.5 hrs.
We can write 4.5 hrs as 9/2 hrs. <-- I hope this is what you expect.
Now finding the avg speed.
1. Total distance = 320 km.
2. Total time taken = 4.5 hrs.
Avg Speed = 320/4.5 = 71.11111... km/hr
Note: Both methods are giving the same answer. |
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Komal said:
(Sat, Jul 10, 2010 08:52:50 AM)
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| THANKS TO SUNDER WHO GIVES A GOOD SOLUTION |
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Renuka said:
(Tue, Nov 9, 2010 10:22:15 AM)
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| Hi Sundar, very nice explaination, thank you so much. |
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Priya said:
(Mon, Nov 29, 2010 09:31:50 AM)
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| @sunder Thanks. |
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Prveen Bilimoga said:
(Thu, Dec 9, 2010 03:50:13 PM)
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| I have a doubt, can we do like this, the first 160 hrs is 64 km speed, and the second hr is 80, total 144. so 144/2 = to 72 |
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Kapil said:
(Mon, Dec 27, 2010 11:56:29 PM)
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Since distance is same,so
avg speed= 2xy/(x+y)
avg s= (2*64*80)/(64+80)
=71.11 |
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Jai said:
(Fri, Mar 18, 2011 01:12:21 PM)
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| Can you explain how 9/2 hours came ? |
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Prajweetha said:
(Tue, May 3, 2011 05:58:00 AM)
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Hello jai,
By simplyfying 160/64 we will get 5/2, while 160/80 becomes 2/1
By taking 2 as LCM we will get 5+4/2=9/2 |
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Vivek said:
(Sat, Jul 23, 2011 03:41:04 PM)
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Hi @Jai
5/2*2/1=by cross multiplication
We have get 5+4/2=9/2 |
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S. M. said:
(Tue, Aug 2, 2011 09:42:24 PM)
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Simple method :- (64+84)/2 =72
Thus on safer side,
we can go with C.) 71.11 km/hr |
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Sugumaran said:
(Mon, Aug 8, 2011 10:26:09 PM)
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Hai praveen and S. M.
Your method is not suitable for all cases. Please avoid this method for solving this type of questions. |
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Fatima said:
(Tue, Oct 18, 2011 02:47:31 PM)
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| Thank you so much Sundar. |
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Elumalai said:
(Sun, Nov 27, 2011 01:43:04 PM)
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| Thank you so much Sundar. |
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