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View Answer
Shortcut:
A carriage driving in a fog passed a man who was walking at the rate of a km/hr in the same direction. If he could see the carriage for t hours and it was visible to him upto a distance of 'n' km, then the distance travelled by the carriage in t hours is (at + n) metres and speed of the carriage is
a +
n
/
t
km/hr
t = 3 min =
3
/
60
=
1
/
20
hrs
n = 200, m =
200
/
1000
=
1
/
5
km
Here, a = 4, t =
1
/
20
, n =
1
/
5
Using these values in the shortcut, we get:
Required speed = 4 +
1/5
/
1/20
= 4 +
20
/
5
= 4 + 4 = 8
Hence, the speed is 8 km/hr.
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