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Question

A man can row three- quarters of a kilometer against the stream in 11.25 minutes and down the stream in 7.5 minutes. The speed ( in km/hr) of the man in still water is-

4 km/hr

5 km/hr

6 km/hr

6.5 km/hr

None of these

ANSWER : 2

Descrption

<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Let the speed of the man and flow of the stream U and V respectively.</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Distance  =  3/4 km</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Time taken to go upstream  =  11.25 min  =  11.25/60 hr</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Conbined speed upstream  =  (3/4) / (11.25/60)  =  4 km/hr</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or,&nbsp; U - V = 4</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or, V = U - 4</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Time taken to go downstream  =  7.5 min  =  7.5/60 hr</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">Conbined speed downstream  =  (3/4) / (7.5/60)  =  6 km/hr</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or, U  +  V = 6</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or, U  +  U - 4 = 6</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or, 2U = 6  +  4</span></p>
<p><span style = "box - sizing: border - box; font - size: 18px; color: #212529; font - family: bangla, sans - serif; text - align: justify; background - color: #ffffff;">or, U  =  10/2  =  <strong>5 km/hr</strong></span></p>

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