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How much time did it take a certain car to travel 400

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KarishmaB

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16 Oct 2018, 01:02

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nitesh50

VeritasKarishma

Yellow22

How much time did it take a certain car to travel 400 km?

1) The car travelled the first 200 KM in 2.5 hrs?
2) If the Car's average speed was 20 KM per hour greater than it was, it would have travelled the 400 KM in 1 hour less time than it did.

I guess the solution is already clear to you.

Just for intellectual purposes, look at an alternative method:

If the car actually took t hours to cover 400 km, in the last 1 hour, the car travels a distance which is equal to 20*(t - 1) km
This must be the distance it covered in each hour since we are considering average speed.
400 = 20*(t - 1)*t
t(t - 1) = 20
t = 5 hrs

Hi VeritasKarishma
The solution appears to be way shorter, but I don't understand a certain aspect.

"in the last 1 hour, the car travels a distance which is equal to 20*(t - 1) km"
THis is the part I am confused about. The speed has been increased by 20. SO the time taken has been reduced by 1 hour. So the distance that is covered from this increase in speed is:20(t-1).
This is the total extra distance. so then what do you mean when you say:
1." IN the last 1 hour"
2.400 = 20*(t - 1)*t (why are we then multiplying by t again)

Regards

Try this:

Attachment:

Ques1.jpeg [ 47.89 KiB | Viewed 2946 times ]

Focus on the (t - 1)th hr. In the hypothetical case, the total distance covered is 20*(t - 1) extra. This is the distance that in current case would have been covered in the last hour. That is why we need 1 hr extra in current case. Since speed S is same every hour, in the last hour too, distance covered in current case would be S, same as distance covered in every hour.
So S = 20*(t - 1) = Distance covered every hour in our current case.

Since we take t hrs to cover the entire distance in current case, 400 = 20*(t - 1)*t

sanjeevsinha082

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29 Jun 2021, 05:14

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1). Insufficient, no idea about the car's speed for the next 200 kms
2) (Actual speed + 20) * (actual time - 1 hour) = 400 kms = actual speed * actual time
Can solve for actual time
Answer is B

RastogiSarthak99

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17 May 2022, 10:53

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my 2 cents on this:

St1 is clearly insufficient. I don't think we can assume the speed derived from F1 is going to be the same for the next 200km travelled. Insufficient

St2: Average Speed = Total Distance/Total Time; meaning (400/t)/t-1; Eventually equating Total Distance/Total Speed = Time Taken, we get a fancy quadratic equation others (Bunuel ++) have come up with. I came up with something similar, but knowing there is only one variable, I didn't solve for it. Left it there. Sufficient.

findingmyself

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23 Jun 2025, 12:06

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What we need to find out is Time T which is 400/Speed X

It is easy that we can eliminate the first statement since remaining 200 Kms the car can travel in any speed hence insufficient.

Statement 2 tells that 400/(X+20)={400/X}-1
Solving this equation, we will get X and using that we can find 400/X, thus statement 2 itself is enough.

DSGB

How much time did it take a certain car to travel 400 kilometers?

(1) The car traveled the first 200 kilometers in 2.5 hours.
(2) If the car's average speed had been 20 kilometers per hour greater than it was, it would have traveled the 400 kilometers in 1 hour less time than it did.