Cars

[Thorak]

 

Bill and William have decided to pull out his old cars from garage, in order to try how fast still they are. They did everything in form of contest, so they have dealed to stand in the start line and do a certain distance with cars in full throttle. Of course win that one, who reach the finish line first. When they reached the finish line they found out, that the car of Bill is 1,2 times faster, than the car of William. William has reached the finish line about 1 minute and 30 seconds later, than Bill. The bill´s car has reached in this given distance 60km/h speed in average.

The question is: How long have to be this distance that they have passed, if we know the above said data? Enter the result in kilometers.

 

[wolfgang]

7.5 Km

[dgreening]

Bill and William have decided to pull out his old cars from garage, in order to try how fast still they are. They did everything in form of contest, so they have dealed to stand in the start line and do a certain distance with cars in full throttle. Of course win that one, who reach the finish line first. When they reached the finish line they found out, that the car of Bill is 1,2 times faster, than the car of William. William has reached the finish line about 1 minute and 30 seconds later, than Bill. The bill´s car has reached in this given distance 60km/h speed in average.

The question is: How long have to be this distance that they have passed, if we know the above said data? Enter the result in kilometers.

SpeedB = 60 km/hr = 1.2 x SpeedW [km/hr] = 1 km/ min

Therefore SpeedW = 60/1.2 [km/hr] = 50 [km/hr] = 5/6 km/ min

TimeW = D [km] /SpeedW [km/min] = D/SpeedW [min] = D/(5/6) min = 6D/5 min = 1.2 D min

Time B = D [km] /SpeedB [km/min] = D/SpeedB [min] = D/(1) min = D min

Since TimeW – TimeB = 1.5 min

Then (1.2 – 1)D min = 0.2D min = 1.5 min

Therefore D = 1.5/0.2 km = 1.5*5 = 7.5 km