Aptitude_Q&A_02

21. In a flight of 600 km, an aircraft was slowed down due to bad weather. Its average speed for the trip was reduced by 200 km/hr and the time of flight increased by 30 minutes. What is the duration of the flight?

1 hour? 2 hours? 3 hours? 4 hours?
 
  Solution:
3 hrs. and 4 hrs. are too large as the average speed is to be greater than 200 kmph.
Test 1 hr.
Time is 1 hr., so Normal speed is 600 kmph.
Slower speed is 400 kmph. and time is 1 hr 30 min.
So flight time increase is 30 min. and this fits the bill.


22. A man completes a journey in 10 hours. He travels first half of the journey at the rate of 21 km/hr and second half at the rate of 24 km/hr. Find the total journey in km.
 
 Solution:
[Note the simplification / solution below!]
  Let half the distance be d km.
d is calculated mentally! [Explanation below.]
Equating total travel time:


Multiply everything by 3:

Multiply everything by 7 x 8:
8d + 7d = 1680

Solving d = 112
Total journey is 224 km.
 
An Alternative Solution:
 'An Useful RULE':
If two equal distances are covered at two different speeds s1 and s2 the average speed for the whole (double distance) journey is
  av speed (1K)
 Solution:
Average speed for the total, 10 hrs. journey, is 22.4 kmph;
Total journey is 22.4 x 10 = 224 km.


23. The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, then the speed of the first train is:

70 kmph., 2) 75 kmph., 3) 84 kmph., 4) 87.5 kmph.
 
 Solution:
Speed of 2nd train is 400/4 = 100 kmph.
Using the ratio, speed of 1st train 7 of 8 parts;
seven-eighth of 100 = 87.5 kmph.
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24. A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. What is the average speed for the first 320 km of the tour?
 
 Solution:
 Equal distances at different speeds:
 
Average speed is misc calc 01 (1K) kmph


25.
A car travelling with Fr_5_7 (1K) of its actual speed covers 42 km in
1 hr 40 min 48 sec. Find the actual speed of the car.
 
 Solution:
One-Step Solution!
The beauty of the Calculation!!
Apt_Q&A_021
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