DXC Quants Problems on Trains Quiz 2

Answer: A

Explanation:

Let the distance between home and office be x.

Let the actual time to reach be t.

Thus, x/10 = t + 12 ---- (1)

and  x/14 = t - 30 -----(2)

Solving equations 1 and 2, we get

x = 135 m

Answer: B

Explanation:

Here, Change in time = 10 and a/b = 7/5

We have, change in time = (b/a - 1) x original time 

=> Original time = Change in time/(b/a - 1)

=>10(7/5 - 1) = 4 minutes.

Answer: B

Explanation:

 

Let the partial distance covered at 50 kmph be x

Let the another partial distance covered at 80 kmph be (500 - x)

Thus, x/50 - (500 - x)/80 = 10

=> x/50 + (500 - x)/80 = 10

=> 8x - 5x + 2500 = 4000

=> 3x = 1500 

=> x = 500

Answer: D
Explanation:
Charlie Puth first , he covers the distance = 50 kmph x 1 hr = 50 km
Shawn Mendes started after 1 hour.
Relative Speed of of both = 60 kmph - 50 kmph = 10 kmph
so, they will meet in = 50/10 = 5 hours.

Answer: B
Explanation:
Let the time taken to reach the destination be 4x hours. Total distance = 60 * 4x = 240x km
He covered 2/3 * 240x = 160x km in 1/4 * 4x = x hours
So, the remaining 40x km, he has to cover in 2x hours would be required speed = 40x / 2x = 20 kmph

Answer: D
Explanation:
Downstream speed= 8 + 2 = 10 km/hr
Upstream speed= 8 - 2 = 6 km/hr
Let distance traveled = X
(X/10)+(X/6)= 8
X = 30 kms
Total distance is 30+30 = 60 kms

Answer: B
Explanation:
Downstream speed =20/10 * 60 = 120 km/hr
4:1 = 4x : 1x
Downstream speed = 4x + x = 5x
Upstream speed = 4x - x = 3x
5x = 120; x = 24
so Upstream speed = 3*24 = 72 km/h
Time = 20/72 * 60 = 50/3 mins

Answer: B
Explanation:
Let the speed of the man in still water be x kmph.
Then,
Speed of the man downstream = (x + 10) kmph,
Speed of the man upstream = (x – 10) kmph.
(x + 10)*3 = (x – 10)*7/2
X = 130 kmph

Answer: C
Explanation:
Speed downstream = 5/x
Speed upstream = 4/x
40/(10/x) + 40/(8/x) = 18
x = 2
So, Speed downstream = 2.5 km/hr, Speed upstream = 2 km/hr
Rate of the stream = 2 * 2 = 4 km/hr

Answer: B
Explanation:
Speed of Chris Evans in still water = x = 10 km/hr.
Let the rate of flow of the river = y km/hr.
Speed of Chris Evans upstream = 10 - y
Speed of Chris Evans downstream = 10 + y
90/(10+y) + 90/(10-y) = 24
⇒ y = 5