Jim paddle from one shore of a lake three miles wide at 4 mph, and john paddles from the opposite shore at 5 mph. how long will they travel before they meet?

Let us assume that the distance travelled by Jim to meet John = X miles
Then the distance travelled by John to meet Jim = (3 - X) miles
We already know the equation
Time = Distance travelled/ Speed
Then for Jim,
Time = X/4
For John
Time = (3 - X)/5
As they meet, so they must have travelled the same amount of time.
Then
X/4 = (3 -X)/5
X = (12-4X)/5
5X = 12 - 4X
9X = 12
X = 12/9
  = 4/3
  = 1.33 miles
Now our target is to find the amount of time after which Jim and John meet.
 Then
Time = X/4
         = 1.33/4
          = 0.33325 hours
         = (0.33325 * 60) minutes
         = 19.995 minutes.
So it can be safely assumed that Jim and John will meet after a period of 20 minutes.

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