Question

A thief runs with the uniform speed of 50m/min. After 2 minutes, a policemen runs after the thief to catch him. He goes with a speed of 60 metres in first minute and increase his speed by 5m/min every succeeding minute. After how many min the policemen will catch the thief.

Answer 1

Speed of the theif is 50 m/min
In 2 mins, the theif covers 100 m.
After 2 mins, the policeman runs to catch him, so in the third minute the policeman covers 60 m.
In the third minute the thief would cover 150 m.

Now policeman increases his speed by 5 m/ min (Student be careful units for speed is 5 m/min NOT just metres)
So, in the fourth minute:
Distance covered by policeman = 60 + 65 = 125 m
Distance covered by thief = 200 m

In the fifth minute:
Distance covered by policeman = 125 + 70 = 195 m
Distance covered by thief = 250 m

In the sixth minute:
Distance covered by policeman = 195 + 75 = 270 m
Distance covered by thief = 300 m

In the 7th minute:
Distance covered by policeman = 270 + 80 = 350
Distance covered by thief = 350 m
Hence, after 7 minutes the policeman will catch the thief.