উত্তর সিলেক্ট করলে সঠিক ও ভুল দেখাবে।
ব্যাখ্যা ও সঠিক সমাধান
উত্তর:
1.6 mph
Let towards upstream he swims at v1 mph and towards downstream he swims at v2 mph . '. v1 = 1 and v2 = 4 Now, his average speed = 21v1 + 1v2 = 211 + 14 = 21 + 14 = 254 = 254 = 2 × 43 = 85 = 1.6 mph[Rule of harmonic mean ]Total 5 mph swims 8 mitres 58 1.6 mph 53030 ×