Question

You and a friend each drive 100 km. You drive 135 km/hr while your friend drives 85 km/hr. How many minutes will you wait before they arrive?

Answer 1

Assuming you and your friend start driving at the same time and drive at your constant speeds, then you would have to wait `~~26` minutes.

Explanation:

Since you are driving at `"135km/hr"`, it takes you

`(100cancel "km")/(135cancel "km""/h")=20/27"h"` to reach to the place.

Since your friend is driving at `"85km/hr"`, it takes them

`(100cancel "km")/(85cancel "km""/h")=20/17"h"` to reach to the place.

Now, we need to subtract the times to calculate for the waiting time. We must take the longer time and subtract it by the smaller time.

`20/17"h"-20/27"h"=200/459"h"`

To find the amount of minutes, we multiply the number of hours by `60`.

`200/459"h"=200/459*60=26.14 \ "min"`

Now, we can round off to the nearest whole number so that the answer is more reasonable

`26.14 \ "min" ~~ 26 \ "min"`

So, you would have to wait around `26` minutes before your friend arrives.