Here is a problem solving. I need the answer to it and why? A naval flotilla is steaming at a constant 12...?

Question

A naval flotilla is steaming at a constant 12 knots, i.e 12 miles per hour.
A speed boat leaves the flotilla, going on ahead to reconnoitre.
It travels at 24 knots. After covering 60 miles the speed boat turns round to go back and rejoin the flotilla.

How long is it from the time the speed boat leaves the flotilla to the time that it rejoins it? (Assume all boats travel at constant speed).

Answer 1

If the speedboat is doing a constant 24 knots, then it will take it 60 miles/24 knots = 2.5 hours to reach it's farthest point. In that time, the flotilla will travel 12 knots(2.5 hours) = 30 miles, so the speedboat and the flotilla will be the remaining 30 miles apart. When the speedboat turns around, it will be approaching the flotilla at a relative (24 + 12) = 36 knots. To cover 30 miles at 36 knots takes 30/36 hours = 50 minutes. So - the speedboat will take 2.5 hours + 50 minutes = 3 hours and 20 minutes to return.

Answer 2

After covering 60 miles, the time when the speed boat go to is 60/24 = 2 hour 30 mins.
Thus, flotilla also go with 2 hour 30 mins, i.e it go 12 * 2.5 = 30 miles.
The distance of two boats after 2 hour 30 mins is 60 - 30 = 30 miles.
Assume t is the time that two boats have to go to rejoin.
Then, 12*t + 24 * t = 30
Or, t = 30/36 = 5/6
The total time that it rejoin is 5/2 + 5/6 = 10/3 = 3 hours 20 mins

Answer 3

60/24 = 2.5 hours time for speedboat to travel 60miles at 24mph
12 (2.5) = 30 miles traveled by flotilla in the same 2.5 hours
60 - 30 = 30 miles distance between flotilla and speedboat
30 / (24 + 12) = 50 minutes time it takes for speed boat and flotilla to meet

2.5 hours + 50 minutes = 150 minutes + 50 minutes = 200 minutes OR 3 hrs 20 minutes

Answer 4

Ship speed=12 miles/hr
Boat speed=24 miles/hr

time taken by boat to go 60 miles=60/24=2.5 hors
distance travelled by ship in 2.5 hours=30 miles
hence boat needs to cover only half distance now
hence time taken by boat to cover 30 miles =1.25 hr
TOTAL=3 hr 45 min