A boat goes down stream at 50 km/hr and upstream at 45 km/hr. Then the speed of the stream (in km/hr) is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2.5
Let the speed of the boat in still water be \( u \) and that of the stream be \( v \). Then
\( u+v=50 \)
\( u-v=45 \)
Subtracting, \( 2v=5 \), so \( v=2.5 \) km/hr.
Tip: Half the sum, \( \frac{50+45}{2}=47.5 \) (Option 4), is the speed of the boat in still water; the speed of the stream is half the difference.
CBSE Applied Mathematics (Class XII):
Boats and Streams
