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Q:

A person goes to his office at 1/3rd of the speed at which he returns from his office. If the average speed during the whole trip is 12 m /h . what is the speed of the person while he was going to his office?

A) 10 B) 6
C) 8 D) can't be determined

Answer:   C) 8

Explanation:

u = k , v= 3k 

 \inline \therefore \frac{2uv}{u+v}\: \: \Rightarrow \frac{2\times k\times 3k}{(k+3k)}=12

\inline \Rightarrow 1.5k = 12

\inline \Rightarrow k=8km/h

 

Q:

A thief goes away with a MARUTHI car at a speed of 40 kmph. The theft has been discovered after half an hour and the owner sets off in a bike at 50 kmph when will the owner over take the thief from the start ?

A) 2 hrs 10 min B) 2 hrs
C) 2 hrs 5 min D) 2 hrs 30 min
 
Answer & Explanation Answer: B) 2 hrs

Explanation:

|-----------20--------------------|
50                           40

Difference = 20kms

Relative Speed = 50 – 40 = 10 kmph

Time = 20/10 = 2 hours.

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Q:

A boatman can row 96 km downstream in 8 hr. If the speed of the current is 4 km/hr, then find in what time he will be able to cover 8 km upstream ?

A) 1.5 hrs B) 1 hrs
C) 2.5 hrs D) 2 hrs
 
Answer & Explanation Answer: D) 2 hrs

Explanation:

Speed in downstream = 96/8 = 12 kmph

Speed of current = 4 km/hr

Speed of the boatman in still water = 12 – 4 = 8 kmph

Speed in upstream = 8 – 4 = 4 kmph

Time taken to cover 8 km upstream = 8/4 = 2 hours.

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1 21
Q:

A boat takes 19 hours for travelling downstream from point A to point B and coming back to a point C which is at midway between A and B. If the velocity of the stream is 4 kmph and the speed of the boat in still water is 14 kmph, what is the distance between A and B ? 

A) 180 km B) 160 km
C) 140 km D) 120 km
 
Answer & Explanation Answer: A) 180 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.

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1 10
Q:

A boatman can row 3 km against the stream in 20 minutes and return in 18 minutes. Find the rate of current ?

A) 1/3 kmph B) 2/3 kmph
C) 1/4 kmph D) 1/2 kmph
 
Answer & Explanation Answer: D) 1/2 kmph

Explanation:

Speed in upstream = Distance / Time = 3 x 60/20 = 9 km/hr.

Speed in downstream = 3 x 60/18 = 10 km/hr

Rate of current = (10-9)/2 = 1/2 km/hr.

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1 7
Q:

A person takes 20 minutes more to cover a certain distance by decreasing his speed by 20%. What is the time taken to cover the distance at his original speed ?

A) 1hr B) 1 hr 20 min
C) 1 hr 10 min D) 50 min
 
Answer & Explanation Answer: B) 1 hr 20 min

Explanation:

Let the distance and original speed be 'd' km and 'k' kmph respectively.

d/0.8k - d/k = 20/60 => 5d/4k - d/k = 1/3

=> (5d - 4d)/4k = 1/3 => d = 4/3 k

Time taken to cover the distance at original speed

= d/k = 4/3 hours = 1 hour 20 minutes.

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