scorpio2804

 Profile Answers by scorpio2804 

• Feb 23rd, 2006

 

120 MPH

kamsach100

 Profile Answers by kamsach100 

• Feb 24th, 2006

 

Total Distance = 4Km

30Mph = 30 (1.6) Kmph = 48 Kmph

Total time = (2/48)+(1/60)+(1/x)

Let that x be the speed with which ,he crosses the 4th side.

Average speed is given = 60 Kmph

Therefore,

Average Speed = Total Distance / Total Time

60 = 4 / { (2/48)+(1/60)+(1/x) }

On solving for "x",We get

x = 120 Kmph

THE PERSON TO HAVE FIRST REPLIED GAVE 120 MPH......... THAT IS WRONG

mrbene

• Apr 7th, 2006

 

This question is meant to be: 2 sides at 30 km/h, 1 side at 60 km/h, what speed for the 4th side for average speed of 60 km/h (consistant speed). The trick is the total time already spent travelling is equal to or more than the maximum time spent to get the desired average speed. In this example, the total perimeter is 4 KM. In order to travel around the entire perimeter at 60 km/h (1 km/minute), it has to be done in 4 minutes. However, at 30 km/h (0.5 km/minute) for the first two sides, those 4 minutes are already used - and we're through 5 after the third side, leaving our man trying to travel back in time while covering the last side. However, as presented, the first two sides are travelled at 30 mph or 48.27 km/h (0.8045 km/minute). This means the first two kilometers are travelled in 2 minutes and 29.16 seconds, and the third in 1 minute (as above). Since there are 30.84 seconds remaining, the man can kick up the pace and travel at 116.73 km/h for the last stretch - for the win!

sid

• Apr 14th, 2006

 

ans is 180 kmph

By solving in the same manner as done above

saleemkhan

 Profile Answers by saleemkhan 

• Apr 15th, 2006

 

avg speed = speed in all the four sides/4 so that60=(30+30+60+x)/4,on solving this u will get the value of x=120 that is correct answer

saramjit singh

• Jul 6th, 2006

 

i think its ans is 179.14km/hr.

(x+.03+.03+60)/4=60

ashma hans

• Sep 27th, 2006

 

In my opinion,the answer should be 179.94Km/hr.

Because

Average speed=Total speed/4

30m/hr=.03Km/hr

60=(.03+.03+60+x)/4

x=179.94Km/hr

Sonalika Ghosh

• Oct 6th, 2006

 

correct answer is 179.94 KMPh

(x+0.03+0.03+60)/4=60

x = 179.94 KMPh

bonvamsi

 Profile Answers by bonvamsi 

• Feb 27th, 2007

 

since it is a square..all the side r equal....at each side place the speed at wich he has travelled....2 side with 30kmph each nd the 3rd with 60kmph....let he traverse the 4th side with x kmph....avg speed is 60kmph....wich implies (30+30+60+x)/4 = 60....hence x = 120 kmph.

naveen saxena

 Profile Answers by naveen saxena 

• Jun 8th, 2007

 

What is the reason for multiplying 1.6 with 30 to get 48.

Why did you multiply 1.6.

If you dont mind can you explain me.

Rameswar Reddy

• Aug 15th, 2007

 

Distance of One Mile is equal to 1.6 Kilometers 

1 Mile = 1.6 Km
1 Hector = 2.5 Acres

Mostly in abroad they measure in miles instead of kilometers. For confusion, they gave parameters in different measures. The question is 100 % right.

mrbene

 Profile Answers by mrbene 

• Aug 24th, 2007

 

1 mile = 1.609344 KM. 

My original answer to the asked question is 116.73 km/h, which is correct to more decimal points than the 120 km/h. 

The original question is wrong, in my books, since it has a solution.  Properly asked, the question is:

Going around a fixed circuit.  First lap at speed (velocity) v/2, second lap at speed v, how fast must the 3rd lap be completed in order for the average speed of all three laps to be v? 

The answer to this question is "infinitely fast, due to the 3rd lap needing to be completed in exactly 0 seconds."

For lap 1, velocity equals distance over time (V = D/T).  Since the distance is fixed, if velocity is halved, time is doubled (V/2 = D /(2T) ).  This means that lap 1 took 2T. 

For lap 2, we have simply taken T. 

At this point, we have done 2D (twice around the course) in 3T (2T from lap 1, 1T from lap 2).  In order to achieve an overall V after 3D, we have to have only used 3T.  IE, lap 3 must complete D in 3T - 3T, or 0T.  Since any variable multiplied by 0 is 0 (0 x T = 0), and since any variable divided by 0 is infinity (V = D / 0, V = infinit), the speed for the final lap would have to be infinitely fast. 

At least, if the question were asked by me :P

/mrbene

kartheek07

 Profile Answers by kartheek07 

• Jan 22nd, 2008

 

here average of four side speed is 60kmph
so (first side+secon+third+fourth)/4=60
(0.03+60+x)/4=60
ANS=179.97kmph

mrbene

 Profile Answers by mrbene 

• Jan 22nd, 2008

 

Everyone other than me is wrong so far, since they are treating speed as a single dimension instead of treating it properly as two (time and distance). 

In order to travel at 60 km/h, the man must travel 60 km in one hour.  This translates into 60 km in 60 minutes, 1 km in 1 minute, or the total 4 km in 4 minutes. 

---

If we assume that the initial question was mis-typed and was meant to be "30 km/h for the first two sides and 60 km/h for the 3rd side", we get the following:

Side 1: 1km at 30 km/h = 2 minutes
Side 2: 1km at 30 km/h = 2 minutes
Side 3: 1km at 60 km/h = 1 minute

Therefore, in order to achieve an average speed of 60 km/h, the man would have had to have finished Side 4 at the moment he finished Side 2.  The best possible would be if he completed:

Side 4: 1km at infinite km/h = 0 minutes

He has now completed 4 km in 5 minutes, and has only achieved an average speed of 48 km/h. 

---

If we assume the initial question was meant to mix mph and km/h, the first step is to translate miles per hour into kilometers per hour.  30 mph is 48.27 km/h. 

Side 1: 1km at 48.27 km/h = 1 minute and 14.58 seconds
Side 2: 1km at 48.27 km/h = 1 minute and 14.58 seconds
Side 3: 1km at 60 km/h = 1 minute

He has now completed 3 km in a total of 3 minutes and 29.16 seconds.  Since the goal is to complete 4 km in 4 minutes, there are 30.84 seconds remaining to travel 1 km:

Side 4: 1km at 116.73 km/h = 30.84 seconds. 

---


So my answers stand (and are backed by mathematics): 

• If the question was mis-typed, and was meant to be "km/h" throughout, the man can not acheive an average speed of 60 km/h, no matter how fast he travels on the last stretch. 
• If the question is properly typed, the man must travel 116.73 km/h. 

In both cases, the key to understanding the question is understanding that "speed" must be split into its two dimensions (distance and time) before performing averages. 

gachiranjeevi

 Profile Answers by gachiranjeevi 

• Dec 29th, 2008

 

Average SPEED IS 60 KMPH, I.E 60 KMS PER 60 MIN... SO 1 KM IN 1 MIN. AS SQUARE SIDES ARE 1 KM EACH..TOTAL TIME TAKEN SHOULD BE 4 MIN. NOW FIRST 2 SIDES..IT IS MPH, NOT KMPH 1 MPH = 1.609344 KMPH SPEED 30 MPH = 30*1.609344 KMPH = 48.28032 KMPH WHICH MEANS PER 1 KM, IT TAKES 1.2 MIN(72 SEC) SO FIRST TWO SIDES=TWO KMS=72+72=144 SECS. 3RD SIDE=1 KM=1 MIN=60 SECS. TOTAL TIME TAKEN FOR 3 SIDES=144+60 =204 SECS. SO 4TH SIDE SHOULD BE COVERED IN 240 SEC-204 SECS=36 SECS..
SO 1 KM IS TRAVELED IN .001 HR..SO SPEED IS 100 KMPH(1/.001=1OO KM/HR)