বিসিএস, ব্যাংক, প্রাথমিক শিক্ষক ও সকল সরকারি চাকরির বিগত সালের প্রশ্ন ও অধ্যায়ভিত্তিক নির্ভুল সমাধান
Solution:
Speed in still water = 12 km/h
Speed of the stream = x km/h
Let the distance travelled is = D km
Time taken upstream = 2 × (Time taken downstream)
D/(12-x) = 2 × {D/(12+x)}
⇒ 1/(12-x) = 2/(12+x)
⇒ 12 + x = 24 - 2x
⇒ 3x = 12
∴ x = 4
So, Speed of the stream = 4 km/h
Solution:
Train 1 length = 100 meters
Train 2 length = 100 meters
Total distance = (100 + 100) = 200 meters
Speed of Train 1 = 72 km/h = 72 × (5/18) m/s = 20 m/s
Speed of Train 2 = 54 km/h = 54 × (5/18) m/s = 15 m/s
Relative speed = (20 + 15) = 35 m/s
Time = (200/35) = 5.71 seconds = 5.7 seconds
Solution:
Train length = 240 meters
Time to pass a pole = 15 seconds
Speed = (240/15) m/s = 16 m/s
Total distance to be covered (train + platform) = 240 + 300
= 540 meters
So, Time = 540/16 = 33.75 seconds
Solution:
Speed of the swimmer in still water = 4 km/h
Speed of the current = 2 km/h
Distance one way = 12 km
Downstream Speed = 4 + 2 = 6 km/h
Upstream Speed = 4 - 2 = 2 km/h
Time taken downstream = 12/6 = 2 hours
Time taken upstream = 12/2 = 6 hours
Total time = 6 + 2 = 8 hours
Solution:
Speed of the swimmer in still water = 4 km/h
Speed of the current = 2 km/h
Distance one way = 12 km
Downstream Speed = 4 + 2 = 6 km/h
Upstream Speed = 4 - 2 = 2 km/h
Time taken downstream = 12/6 = 2 hours
Time taken upstream = 12/2 = 6 hours
Total time = 6 + 2 = 8 hours
Solution:
Speed of athlete = 200 m/24 sec
= (200 × 18)/(5 × 24) = 30 km/hour
Solution:
Let the speed of the man be x km/h
Distance covered by the man in 10 min = Distance covered by the bus in 5 min
According to the question
⇒ x × 10/60 = 30 × 5/60
⇒ 10x = 150
⇒ x = 15 km/h
∴ Speed of the man is 15 km/h
Solution:
Given,
Man covers half of his journey at 12 km/h
The remaining half at 6 km/h
His average speed is = (2 × 12 × 6)/(12 + 6)
= 144/18 = 8 km/h
