A car travels from city A to city B on a freeway that has sections that are under construction. In the unimproved sections, the speed limit is 80 kph. In the sections under construction, one side is completed and the speed limit is 90 kph, while the other side still being worked on has an imposed speed limit of 72 kph. It takes the car 2 hours to get from A to B, but 3 hours to get back.
How far is it from A to B?
How far is it from A to B?
-
Are you sure you've used the correct vales in the question? To travel the same distance in 2/3 of the time, it would require going 3/2 times faster. But 3/2 * 72 kph = 108 kph, faster than is possible. If you solve the system of equations provided by RSS, you get a negative amount of roadway that is unimproved.
-
Let's say the distance covered in unimproved section is x, in section under construction is y.
x/80 + y/90 = 2 hours on the way from A to B.
x/80 + y/72 = 3 hours on the way back.
Solve for x and y, add x and y, and you have the answer.
x/80 + y/90 = 2 hours on the way from A to B.
x/80 + y/72 = 3 hours on the way back.
Solve for x and y, add x and y, and you have the answer.
-
i dont understand. which lane is the car on? the 80kph to B or 90kph to B or 72kph to B