The table shows, for a boat over five days (Monday to Friday), the distance travelled upstream (km), speed of boat (km/h), speed of stream (km/h) and total time (hours). Dashes are missing and to be calculated. Distance upstream = distance downstream; total time = downstream time + upstream time.
| Day | Distance Upstream (km) | Speed of Boat (km/h) | Speed of Stream (km/h) | Total Time (hours) |
|---|---|---|---|---|
| Monday | 320 | — | 4 | — |
| Tuesday | — | — | — | 75 |
| Wednesday | 270 | — | 6 | — |
| Thursday | — | 11 | 7 | — |
| Friday | 324 | — | — | 72 |
On Thursday, the difference between the time taken by the boat to cover X km upstream and (X + 120) km downstream is 26 hours. Had the boat covered the same distance upstream as downstream, then what would have been the difference in the time taken?
The required difference on Thursday is 56 hours.
The boat speed is 11 km/h and stream speed is 7 km/h, so upstream speed is 4 and downstream speed is 18.
The given condition is X over 4 minus (X plus 120) over 18 equals 26.
Solving gives X equals 168 km.
For equal distances, the downstream distance becomes 168 plus 120, that is 288 km.
The new difference is 288 over 4 minus 288 over 18, that is 72 minus 16.
The required difference is 56 hours.
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