Aptitude Discussion

Q. |
A man can row 4.5 km/hr in still water and he finds that it takes him twice as long to row up as to row down the river. Find the rate of the stream. |

✖ A. |
2 km/hr |

✖ B. |
2.5 km/hr |

✔ C. |
1.5 km/hr |

✖ D. |
1.75 km/hr |

**Solution:**

Option(**C**) is correct

Let the speed of the current be $x$ km/hr

Thus upward speed = $(4.5-x)$ km/hr

and downward speed = $(4.5+x)$ km/hr

Let distance travelled be $y$, then for the same distance $y$,

$\text{Time Rowing Upwards}$$=2\times \text{Time Rowing Downwards}$

\(\dfrac{y}{4.5-x}=2 \times \dfrac{y}{4.5+x}\)

⇒ $x=$ **1.5 km/hr**

**Edit:** Thank you **Sid** for pointing out the typo, upwards and downwards speeds have been corrected.

**Muhammad Zeeshan**

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**Sid**

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A correction. Speed downstream is $4.5+x$ and the speed upstream will be $4.5-x$ :)

Thank you Sid for pointing out the typo, I've modified and corrected the solution.

Let man’s upstream rate be x kmph.

Then, his downstream rate= 2x kmph

Rate in still water = 1/2 (2x + x) kmph = 1.5x kmph

So, 1.5x = 4.5 or x = 3

Upstream Rate= 3 km/hr, Downstream Rate= 6 km/hr

Hence, rate of stream = 1/2 (6 – 3) km/hr = 1.5 km/hr