The ratio of the speed of a motorboat to that of the water current is 32 : 8. The boat goes somewhere along the current for 4 hours and 45 minutes. How much time will it take to come back from there?
-
7 hours and 12 minutes
-
6 hours and 18 minutes
-
7 hours and 5 minutes
-
7 hours and 55 minutes
-
None of these
D
Correct answer
Explanation
Speed ratio boat:current = 32:8 = 4:1. Downstream speed = 4+1 = 5 units. Upstream speed = 4-1 = 3 units. Time taken downstream = 4.75 hours. Distance = 5 * 4.75 = 23.75 units. Time taken upstream = 23.75 / 3 = 7.9166 hours. 0.9166 * 60 = 55 minutes. Total = 7 hours 55 minutes.