These are questions about how a native English speaker will naturally interpret the words. To some extent, you may have to let go of your own sense of the
possible interpretations, and learn what the
natural meaning is. Languages can be tricky that way.
When I am in doubt, I commonly try rewording it a little. I'll demonstrate.
Q1 : A man can row 7.5 km/h in still water. If in a river running at 1.5 km/h, it takes him 50 min to row to a place and back, how far off is the place?
DOUBT 1: 50 minutes total or one journey ??
The statement
"it takes him 50 min to row to a place and back"
means
"if he rows to a place and back, it will take him 50 minutes"
The time, 50 minutes, covers the entire
action, and the action is "rowing there and back".
Q2:
A man rows a boat at a speed of 15 mph in still water. Find the speed of the river if it takes her 4 hours 30
minutes to row a boat to a place 30 miles away and return.
DOUBT 2: 30 miles in total or each journey ?
The statement
"it takes her 4 hours 30 minutes to row a boat to a place 30 miles away and return"
means
"if she
rows to a place 30 miles away, and then returns, the total time will be 4 hours 30 minutes"
The distance, 30 miles, is described as how far away the destination is, not to the total distance rowed. The time, 4:30, applies to the entire
action, but the distance describes the
place.
row a boat to a place 30 miles away and return. . What if i read this line in a go ..it makes sense to me 30 miles is both away and return
You could conceivably
force the words to mean that the 30 miles describes a trip "away and return", but I don't think any English speaker would say it in that way.