IBPS RRB Office Assistant (Multipurpose) Prelims practice question
A boatman whose speed in still water is 12 km/h takes 2 hours more to go 32 km upstream than to go the same distance downstream. What is the speed of the stream?
From a IBPS RRB Office Assistant (Multipurpose) Prelims Quantitative Aptitude practice set · Quantitative Aptitude
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Correct answer: (B) 4 km/h
Let stream speed = x km/h. 32/(12 − x) − 32/(12 + x) = 2 ⇒ 32 × 2x/(144 − x²) = 2 ⇒ 64x = 2(144 − x²) ⇒ 2x² + 64x − 288 = 0. Check x = 4: 32/8 − 32/16 = 4 − 2 = 2 ✓. Stream speed = 4 km/h.
हिंदी में प्रश्न
एक नाविक, जिसकी शांत जल में चाल 12 किमी/घंटा है, 32 किमी धारा के प्रतिकूल जाने में उतनी ही दूरी धारा के अनुकूल जाने की तुलना में 2 घंटे अधिक लेती है। धारा की चाल कितनी है?
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सही उत्तर: (B) 4 किमी/घंटा
माना धारा की चाल = x किमी/घंटा। 32/(12 − x) − 32/(12 + x) = 2 ⇒ 32 × 2x/(144 − x²) = 2 ⇒ 64x = 2(144 − x²) ⇒ 2x² + 64x − 288 = 0। जाँच x = 4: 32/8 − 32/16 = 4 − 2 = 2 ✓। धारा की चाल = 4 किमी/घंटा।
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