| Days | Distance Upstream(km) | Speed of Boat(km/hour) | Speed of Stream(km/hour) | Total Time Taken(hours) |
| Monday | 320 | - | 4 | - |
| Tuesday | - | - | - | 75 |
| Wednesday | 270 | - | 6 | - |
| Thursday | - | 11 | 7 | - |
| Friday | 324 | - | - | 72 |
Note: (1) Distance Upstream = Distance Downstream, if not stated otherwise
(2) Total Time Taken = Downstream Time + Upstream Time
On Friday, if the ratio of speed of boat to speed of stream is 2 : 1, then what is the difference between the time taken by the boat to go upstream and to go downstream?