Aptitude Discussion

Q. |
A motorboat whose speed is 15 km/hr in still water goes 30km downstream and comes back in four and a half hours. The speed of the stream is: |

✖ A. |
4.5 km/hr |

✖ B. |
6 km/hr |

✖ C. |
7 km/hr |

✔ D. |
5 km/hr |

**Solution:**

Option(**D**) is correct

Let the speed of the stream be '$s$' km/hr.

Then, upward speed = $(15−s)$ km/hr

and downward speed = $(15+s)$ km/hr

Therefore,

\(\dfrac{30}{(15+s)}+\dfrac{30}{(15-s)}=4.5\)

On solving this equation we get, $s$ = **5 km/hr**

**Edit:** A typo in the solution has been corrected after it was pointed out by **Vejayanantham TR.**

**Vejayanantham TR**

*()
*

Thank you, Vejayanantham for pointing it out. Corrected the typo.

it is not -4.5 , it is just 4.5