# Boats and Streams Questions

A) 1.8h | B) 3h |

C) 4h | D) 5h |

Explanation:

Upstream speed = B-S

Downstream speed = B+s

B-S = 15/5 = 3 km/h

Again B= 4S

Therefore B-S = 3= 3S

=> S = 1 and B= 4 km/h

Therefore B+S = 5km/h

Therefore, Time during downstream = 15/5 = 3h

A) 16 km | B) 18 km |

C) 21 km | D) 25 km |

Explanation:

Let the distance covered be D km.

$\frac{D}{10+4}+\frac{D}{10-4}=5$

$\frac{D}{14}+\frac{D}{6}=5$

10D = 42 x 5 = 210

=> D = 21 km

A) 15 h | B) 16 h |

C) 8 h | D) 20 h |

Explanation:

If t1 and t2 are the upstream and down stream times. Then time taken in still water is given by

$\frac{2\times t1\times t2}{t1+t2}=\frac{2\times 12\times 24}{36}=16h$

A) 8 kmph | B) 6 kmph |

C) 7.5 kmph | D) 5.5 kmph |

Explanation:

Speed of the stream = 1

Motor boat speed in still water be = x kmph

Down Stream = x + 1 kmph

Up Stream = x - 1 kmph

[35/(x + 1)] + [35/(x - 1)] = 12

x = 6 kmph

A) 5 kmph | B) 10 kmph |

C) 15 kmph | D) 45 kmph |

Explanation:

Speed of the boat downstream s=a/t= 60/3 = 20 kmph

Speed of the boat upstream s= d/t = 30/3= 10 kmph

Therefore, The speed of the stream = $\frac{speedofdownstream-speedofupstream}{2}$=5 kmph

A) 180 km | B) 160 km |

C) 140 km | D) 120 km |

Explanation:

Speed in downstream = (14 + 4) km/hr = 18 km/hr;

Speed in upstream = (14 – 4) km/hr = 10 km/hr.

Let the distance between A and B be x km. Then,

x/18 + (x/2)/10 = 19 ⇔ x/18 + x/20 = 19 ⇒ x = 180 km.

A) 1.8 kmph | B) 2 kmph |

C) 2.2 kmph | D) 1.5 kmph |

Explanation:

Speed of Boy is B = 4.5 kmph

Let the speed of the stream is S = x kmph

Then speed in Down Stream = 4.5 + x

speed in Up Stream = 4.5 - x

As the distance is same,

=> 4.5 + x = (4.5 - x)2

=> 4.5 + x = 9 -2x

3x = 4.5

x = 1.5 kmph