A certain river has a current of 3 miles per hour. A boat takes twice as long to travel upstream between two points as it does to travel downstream between the same two points. What is the speed of the boat in still water ?

A 3 miles per hour
B 6 miles per hour
C 9 miles per hour
D 12 miles per hour

Correct Answer: 9 miles per hour

ধরি, C কাজটি করে x দিনে ∴ A " " " " ( x + 9 ) দিনে ∴ B " " " " ( x + 9 - 5 )" = x + 4 " ∴1x + 9 + 1x + 4 = 1x ⇒x + 4 + x + 9(x + 9)(x + 4) = 1x ⇒2x + 13x2 + 13x + 36 = 1x ⇒2x2 + 13x = x2 + 13x + 36 ⇒2x2 - x2 + 13x - 13x = 36 ⇒x2 = 36 ⇒x = 36 ∴ x = 6 ∴ কাজটি করতে Aএর সময় লাগে (6 + 9) দিন = 15 দিন।
Bissoy MCQ
#গণিত #নৌকা ও স্রোত (Boat and stream) #Agrani bank Ltd #Agrani bank Ltd - Senior Officer (Re-exam) - 26.07.2013

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