NCHMCT JEE 2015 Question Paper with solutions for online practice

Let, speed of boat = x km/hr and speed of stream = y km/hr
According to the question,
$\frac{\mathit{d}}{\mathit{y}+\mathit{x}}$ = 2
⇒ 2x + 2y = d ...(i)
and $\frac{\mathit{d}}{\mathit{x}-\mathit{y}}$ = 5
⇒ 5x – 5y = d ...(ii)
2x + 2y = d ] × 5
5x – 5y = d ] × 2
10x + 10y = 5d
10x – 10y = 2d
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20x = 7d
⇒ x = $\frac{7\mathit{d}}{20}$
$2\left(\frac{7\mathit{d}}{20}\right)$ + 2y = d
⇒ 2y = d - $\frac{7\mathit{d}}{10}$ = $\frac{3\mathit{d}}{10}$
⇒ y = $\frac{3\mathit{d}}{20}$
Required ratio = $\frac{\frac{7\mathit{d}}{20}}{\frac{3\mathit{d}}{20}}$ = 7 : 3