If a boat can travel a certain distance downstream in 10 hours and the same distance upstream in 15 hours then what is the speed of the current if the speed of the boat is 10 kmph? यदि एक नाव किसी निश्चित दूरी को धारा के अनुकूल 10 घंटे में और उसी दूरी को धारा के प्रतिकूल 15 घंटे में तय करती है तो धारा की चाल क्या है यदि नाव की चाल 10 किमी./घंटा है ?

Let the distance be D. Downstream speed = (10+c), upstream speed = (10-c). Time = Distance/Speed, so D/(10+c) = 10 and D/(10-c) = 15. Dividing: (10-c)/(10+c) = 10/15 = 2/3. Cross-multiply: 30-3c = 20+2c, so 5c = 10, giving c = 2 km/hr. The current's speed is 2 km/hr. Check: Downstream 12 km/hr covers 120 km in 10 hrs, upstream 8 km/hr covers 120 km in 15 hrs.