Question: I have to be at a certain place at a certain time and find that I shall be 20 minutes too late if I walk at 3 km/hr and 10 minutes too soon if I walk at 4 km/hr. How far I have to walk ?
A
6 km
B
10 km
C
1212 km
D
1623 km
Note: Let the distance be x km
x3-x4=3060⇒x12=12⇒x=6km
Note: New speed=67 of the usual speed.
New time taken=76 of the usual time
(76ofusualtime) - (usual time) = 12 min.
∴16 of usual time = 12 min. or usual time = 72 min.
Question: A car takes 5 hours to cover a distance of 300 km. How much should the speed in km/hr be maintained to cover the same distance in45 th of the previous time ?
A
48
B
60
C
75
D
120
Note: Distance = 300 km.
Time required=(45×5)=4 hours
Speed=(3004)=75 km/hr
Question: Two men start together to walk a certain distance at 3.75 km and 3 km per hour respectively. The former arrives 30 minutes before the later. The distance they walked is :
A
7.5 km
B
10 km
C
12.5 km
D
15 km
Note: Suppose they walked x km.Then,
x3-x3.75=3060⇒0.75x3×3.75=12∴x=3×3.751.5=7.5km
Question: A person travels equal distance with speeds of 3 km/hr, 4 km/hr and 5 km/hr and takes a total time of 47 minutes. The total distance (in km) is :
A
2
B
3
C
4
D
5
Note:x3+x4+x5=4760⇒20x+15x+12x=47⇒x=1
:. Total distance=(1+1+1)km=3km