VeritasKarishma wrote:
Yellow22 wrote:
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
VeritasKarishmaThe 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
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