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Q:

A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is

A) 35.55 km/hr B) 36 km/hr
C) 71.11 km/hr D) 71 km/hr

Answer:   C) 71.11 km/hr

Explanation:

Total time taken    = (160/64 + 160/8)hrs
                           = 9/2 hrs.


Average speed    = (320 x 2/9) km.hr
                         = 71.11 km/hr.

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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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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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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Q:

Two men A and B start from place X walking at 4 ½ kmph and 5 ¾ kmph respectively. How many km apart they are at the end of 3 ½ hours if they are walking in the same direction ?

A) 2 9/7 km B) 3 7/5 km
C) 1 3/4 km D) 4 3/8 km
 
Answer & Explanation Answer: D) 4 3/8 km

Explanation:

Relative Speed = 5 ¾ - 4 ½ = 1 ¼

Time = 3 ½ h.

Distance = 5/4 x 7/2 = 35/8 = 4 3/8 km.

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Q:

Jagan went to another town covering 240 km by car moving at 60 kmph. Then he covered 400km by train moving at 100 kmph and then rest 200 km he covered by a bus moving at 50 kmph. The average speed during the whole journey was ?

A) 36 kmph B) 35 kmph
C) 72 kmph D) 70 kmph
 
Answer & Explanation Answer: D) 70 kmph

Explanation:

By car 240 km at 60 kmph
Time taken = 240/60 = 4 hr.

By train 240 km at 60 kmph
Time taken = 400/100 = 4 hr.

By bus 240 km at 60 kmph
Time taken = 200/50 = 4 hr.

So total time = 4 + 4 + 4 = 12 hr.
and total speed = 240+400+200 = 840 km
Average speed of the whole journey = 840/12 = 70 kmph.

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