Aptitude - Problems on Trains - Discussion

(A's Speed):(B's Speed)= sq.under root a: sq.under root b

@Pawan :

Detailed explanation:
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Formula: Distance = (Speed x Time).

Speed = 90 km/hr

Convert km/hr into m/sec.

Therefore, Speed = (90 x 1000/3600) = 90000/3600 = 25 m/s

Now, Time = 4 hr 40 min

Convert it into secs.

Therefore = (4 x 3600) + (40 x 60 )= 14400+2400 = 16800 secs.

Now, Distance = 25 m/sec x 16800 sec = 25 x 16800 m

= 4,20,000 m [or]

= 420 km. [1000 m = 1 km]

Some short-cut tricks :
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Distance = (Speed x Time)

We can write 4 hr 40 mins = (4 + 40/60) hrs.

So, Distance = 90 x (4 + 2/3)

= (90 x 4) + (90 x 2/3)

= 360 + 60

= 420 km. [or] 420000 m.

Hello please solve this question.

The speed of a train is 90 kmphr, how much distance will it cover in 4 hr 40 min.

One of the smart way of doing the question is by seeing the options itself. Since the first train reach its destination earliest after meeting the second train, then its speed would be greater than the second train and so as the ratio. In the options given above, only in B the ratio of the first train greater than the second.

Ishita narula is correct. Thank you.

@abhisek.

Please be reasonable yaar. Otherwise you will be a laughing stuff to everyone.

How can we calculate the time to cover the total distance, for this sum?

Ishita Narula z correct....

It is a completely wrong answer.

<Case-1> Speed = Distance/Time

(As distance is same, so Speed(S1)= Distance(D)/Time(T1).
Similarly, (S2)= (D)/(T2), Now, (S1)/(S2)=[(D)/(T1)]/[(D)/(T2)]
=[(D)/(T1)]*[(T2)/(D)]
=(T2)/(T1)
So,ratio of speeds is inversely proportional to ratio of times.

<Case-2>

How can (16/9)=(4/3) or (9/16)=(3/4)??? Please Explain???

In Ratio,Proportion and percentage,(9/16)*100 = 56.25%;
But,(3/4)*100 = 75%.

Now, PLEASE EXPLAIN,IS 56.25% = 75% ???

THE CORRECT ANSWER TO THE ABOVE QUESTION IS (16/9) or 16:9.
OR IF WE CONSIDER THE REVERSE RATIO(RECIPROCAL)OF SPEEDS, THEN (9/16) or (9:16).

Here in this question, one train had reached in 9 hrs and another one in 16 hrs.The first train reached faster than the second one ,clearly it should have more speed than the second one, as we know that time and speed are inversely proportional and comparing all answers, 4:3 is most optimal.