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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

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

$\inline&space;\Rightarrow&space;1.5k&space;=&space;12$

$\inline&space;\Rightarrow&space;k=8km/h$

Q:

A bus covers its journey at the speed of 80km/hr in 10hours. If the same distance is to be covered in 4 hours, by how much the speed of bus will have to increase ?

 A) 85 km/hr B) 95 km/hr C) 105 km/hr D) 120 km/hr

Answer & Explanation Answer: D) 120 km/hr

Explanation:

Initial speed = 80km/hr
Total distance = 80 x 10 = 800km
New speed = 800/4 =200km/hr
Increase in speed = 200 - 80 = 120km/hr

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Q:

Joel travels the first 3 hours of his journey at 60 mph speed and the remaining 5 hours at 24 mph speed. What is the average speed of Joel's travel in kmph ?

 A) 38 kmph B) 40 kmph C) 60 kmph D) 54 kmph

Answer & Explanation Answer: C) 60 kmph

Explanation:

Average speed = Total distance / Total time.

Total distance traveled by Joel = Distance covered in the first 3 hours + Distance covered in the next 5 hours.

Distance covered in the first 3 hours = 3 x 60 = 180 miles
Distance covered in the next 5 hours = 5 x 24 = 120 miles

Therefore, total distance traveled = 180 + 120 = 300 miles.

Total time taken = 3 + 5 = 8 hours.

Average speed = 300/8 = 37.5 mph.

we know that 1 mile = 1.6 kms

=> 37.5 miles = 37.5 x 1.6 = 60 kms

Average speed in Kmph = 60 kmph.

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Q:

Two persons start running simultaneously around a circular track of length 600 m from the same point at speeds of 25 kmph and 35 kmph. When will they meet for the first time any where on the track  ?

 A) 54 sec B) 36 sec C) 72 sec D) 11 sec

Answer & Explanation Answer: B) 36 sec

Explanation:

Time taken to meet the first time = length of track/relative speed

Given the length of the track is 600 m

The relative speed = 25 + 35 = 60 kmph = 60 x 5/18 m

Therefore Time = $\inline \fn_jvn \frac{600}{(25+35)\frac{5}{18}}$  = 600/60 x (18/5) = 36 sec.

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Q:

A boy can swim in still water at 4.5 km/h, but takes twice as long to swim upstream than downstream. The speed of the stream is ?

 A) 1.8 kmph B) 2 kmph C) 2.2 kmph D) 1.5 kmph

Answer & Explanation Answer: 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

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Q:

A man can row 6 kmph in still water. When the river is running at 1.2 kmph, it takes him 1 hour to row to a place and back. What is the total distance traveled by the man ?

 A) 4.58 kms B) 6.35 kms C) 5.76 kms D) 5.24 kms

Answer & Explanation Answer: C) 5.76 kms

Explanation:

Speed in still water = 6 kmph

Stream speed = 1.2 kmph

Down stream  = 7.2 kmph

Up Stream = 4.8 kmph

x/7.2 + x/4.8 = 1

x = 2.88

Total Distance  = 2.88 x 2 = 5.76 kms

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