1. A, B and C start at the same time in the same direction to run around a circular stadium. A completes a round in 252 seconds, B in 308 seconds and c in 198 seconds, all starting at the same point. After what time will they again at the starting point ?

1. 26 minutes and 18 seconds

2. 42 minutes and 36 seconds

3. 45 minutes

4. 46 minutes and 12 seconds

Answer & Explanation

Answer:- 4

Explanation :-

Time taken by A to complete the circle = 252 sec.

Time taken by B to complete the circle = 308 sec.

Time taken by C to complete the circle = 198 sec.

They will again at starting together after,

LCM of 252, 308 and 198.

252 = 2 *2 *3*3*7 308 = 2 *2*7*11 198 = 2 *3*3*11

LCM = 2*2*3*3*7*11 = 2772 seconds

=> 46 minutes 12 seconds.

2. The stream of a boat when travelling downstream is 32 km/hr, whereas when travelling upstream it is 28km/hr. what is the speed of boat in still water?

1. 27km/hr

2. 30km/hr

3. 31km/hr

4. Cannot be determined

Answer & Explanation

Answer:- 2

Explanation :-

Speed of boat in still water = (32+28)/2 = 60/2 = 30km/hr

3. A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:

1. 35.55 km/hr

2. 36 km/hr

3. 71.11 km/hr

4. 71 km/hr

5. 69.69km/hr

Answer & Explanation

Answer:- 3

Explanation :-

Time = Distance/speed

Time taken to Complete first 160 km with speed 64 km/h = (160/64) = 10/4 hrs

Time taken to Complete last 160 km with speed 80 km/h = (160/80) = 2 hrs

Total Time = (10/4) + 2 = 9/2 hrs

Time taken for 320 Km = 320/(9/2) = 71.11km/hr

4. A train travelling at 36 kmph completely crosses another train having half its length and travelling in the opposite direction at 54 kmph, in 12 seconds. If it also passes a railway platform in 112 minutes, the length of the platform is :

1. 560 metres

2. 620 metres

3. 700 meres

4. 750 metres

5. 720 meters

Answer & Explanation

Answer:- 3

Explanation :-

Let the length of slower train =x metres

Therefore , the length of faster train = (x/2) meters.

Relative speed = (36 + 54) km/hr = (90×5/18) m/sec = 25 m/sec

3x/(2×25) = 12

3x = 600

x = 200 m

Length of slower train = 200 m

Let the length of platform be y metres

Then, (200 + y)/(36 + 5/18) = 90

200 + y = 900

y = 700 m

Length of platform = 700 m

5. A man travels 35 km partly at 4 km/hr and at 5 km/hr. If he covers former distance at 5 km/hr and later distance at 4 km/hr, he could cover 2 km more in the same time. The time taken to cover the whole distance at original rate is

1. 9 hours

2. 7 hours

3. 9/2 hours

4. 8 hours

5. 10 hours

Answer & Explanation

Answer:- 4

Explanation :-

Let’s assume the man covers first distance in x hrs second distance in y hrs.

Distance = (speed * time) , Therefore ,

4x + 5y = 35 & 5x + 4y = 37

Solving these equations, we get

x = 5 & y = 3

Total time taken = 5 + 3 hrs.

= 8 hrs.