19
Q:

# A thief is noticed by a policeman from a distance of 200 m. The thief starts running and the policeman chases him. The thief and the policeman run at the rate of 10 km and 11 km per hour respectively. What is the distance between them after 6 minutes?

 A) 100 m B) 150 m C) 190 m D) 200 m

Answer:   A) 100 m

Explanation:

Relative speed of the thief and policeman  =  (11 – 10) km/hr = 1 km/hr

Distance covered in 6 minutes  = ${\color{Blue}&space;\left&space;(&space;\frac{1}{60}\times&space;6&space;\right&space;)}$ km   = ${\color{Blue}&space;\frac{1}{10}}$ km = 100 m

${\color{Blue}&space;\therefore&space;}$ Distance between the thief and policeman = (200 – 100) m = 100 m.

Q:

Jagan went to another town covering 240 km by car moving at 60 kmph. Then he covered 400km by train moving at 100 kmph and then rest 200 km he covered by a bus moving at 50 kmph. The average speed during the whole journey was ?

 A) 36 kmph B) 35 kmph C) 72 kmph D) 70 kmph

Answer & Explanation Answer: D) 70 kmph

Explanation:

By car 240 km at 60 kmph
Time taken = 240/60 = 4 hr.

By train 240 km at 60 kmph
Time taken = 400/100 = 4 hr.

By bus 240 km at 60 kmph
Time taken = 200/50 = 4 hr.

So total time = 4 + 4 + 4 = 12 hr.
and total speed = 240+400+200 = 840 km
Average speed of the whole journey = 840/12 = 70 kmph.

1 1
Q:

A son and father goes for boating in river upstream . After rowing for 1 mile son notices the hat of his father falling in the river. After 5 min he tells his father that his hat has fallen. So they turn round and are able to pick the hat at the point from where they began boating after 5min. Find the speed of river  in miles/hours ?

 A) 4 mile/hr B) 6 mile/hr C) 2 mile/hr D) 5 mile/hr

Answer & Explanation Answer: B) 6 mile/hr

Explanation:

Let the speed of river and boat be 'r' m/min and 'b' m/min.
so relative speed in upstream (b-r)m/min and in downstream (b+r)m/min.
Now in upstream distnce covered in 5 min is 5(b-r)miles
so total distnce covered => 1 + 5(b-r)miles in upstream
In downstream distance covered in 5min is 5(b+r)miles
Now 1 + 5(b-r) = 5(b+r)
1+5b-5r = 5b+5r
1 = 10r
r = 1/10 mile/min => 6 mile/hr.

1 27
Q:

Ali and Faizer are 27m apart. They both start walking and meet 9 hrs later, if they travel in the same direction and meet after 3 hrs if they walk in opposite dirction, Ali’s speed must most likely be ?

 A) 9 m/h B) 3 m/h C) 6 m/h D) 12 m/h

Answer & Explanation Answer: C) 6 m/h

Explanation:

let, speed of Ali=X mph and Faizer=Y mph

Now, relative speed when Ali is walking int the same direction with Faizer= (X-Y)mph
hence, according to question, 27/(X-Y)=9 ; solving X-Y=3; --- (1)

Now relative speed when walking in the opposite direction= (X+Y) mph
hence, according to question, 27/(X+y)=3; solving X+Y=9; --- (2)

solving 1 and 2 we get X=6 and Y=3, where X is the speed of Ali.

1 33
Q:

A boat travels 72 km downstream in 8 hours and 84 km upstream in 12 hours. Find the speed of the boat in still water and the speed of the water current ?

 A) 9 and 3 kmph B) 6 and 7 kmph C) 8 and 1 kmph D) 7 and 2 kmph

Answer & Explanation Answer: C) 8 and 1 kmph

Explanation:

Downstream speed = 72km/8hrs  = 9 kmph
upstream speed = 84km/12hrs = 7 kmph
speed of boat = avg of downstream and upstream speeds
speed of boat = (9+7)/2kmph = 8 kmph.
current speed = half of the difference of downstream and upstream speeds
currend speed = (9-7)/2kmph = 1 kmph

1 32
Q:

Two trains start from same place at same time at right angles to each other. Their speeds are 36km/hr and 48km/hr respectively. After 30 seconds the distance between them will be ?

 A) 900 mts B) 300 mts C) 250 mts D) 500 mts

Answer & Explanation Answer: D) 500 mts

Explanation:

Using pythagarous theorem,
distance travelled by first train = 36x5/18x30 = 300m
distance travelled by second train = 48x5/18x30 = 400m
so distance between them =√( 90000 + 160000) = √250000 = 500mts.