GATE Questions

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Given that train K crosses a pole in 30 seconds and train L crosses the same pole in one minute and 15 seconds.

Let the length of train K be Lk and that of train L be Ll

given that Lk = 3/4 Ll

As the train K and L crosses the pole in 30 seconds and 80 seconds respectively,
=> Speed of train K = sk = Lk/30

Speed of train L = sl = Ll/80

Lk = 3/4 Ll
=> sk = 3/4 Ll/(30) = Ll/40

Ratio of their speeds = sk : sl
= Ll/40 : Ll/80

=> 1/40 : 1/80  =  2 : 1

We have 12 months.

In every month we get 28 or more days. 

So that implies we get 28 days in each and every month.

Let the two digits be x & y

From given data in the question, we get

x + y = 3(x - y)

x + y = 3x - 3y

=> 2x = 4y

x/y = 2/1

For having the 2:1, numbers satisfying are

12, 21, 24, 42, 36, 63, 48, 84

From this 36 is eleminated because it is a perfect square and no others are prime or perfect squares.

Hence, there exists 7 such 2-digit numbers => 12, 21, 24, 42, 63, 48, 84.

Given 0.875 and 0.375

0.875 ::

After decimal point there are 3 digits 875

Now, mutiply and divide 0.875 with 1000

$$\begin{gathered} 0.875 x 10001000 = 8751000 \\ Now, this can be reduced to fraction 78 \\ Therefore, 0.875 as fraction = 78 \end{gathered}$$

Similarly,

0.375 :: 

After decimal point there are 3 digits 375

Now, mutiply and divide 0.375 with 1000

$$\begin{gathered} 0.375 x 10001000 = 3751000 \\ Now, this can be reduced to fraction 38 \\ Therefore, 0.375 as fraction = 38 \end{gathered}$$

Now, the distance covered by Chennai express in 2 hrs = 60 x 2 = 120 kms

Let the Charminar Express takes 't' hrs to catch Chennai express

=> 80 x t = 60 x (2 + t)

=> 80 t = 120 + 60t

=> t = 6 hrs

Therefore, the distance away from Hyderabad the two trains meet = 80 x 6 = 480 kms.