An airline has two daily one-way flights operating from Istanbul to Vienna. Each flight takes the same path, and hence covers the same distance D every time. The 1st flight travels at a speed between 600 mph and 800 mph and covers D in 2.5 hours. The 2nd flight travels at a speed between 800 and 1000 mph and covers D in 1.75 hours. Which of the following could be possible value(s) of D?

I. 1500
II. 1620
III. 1750

A. Only I
B. Only II
C. Only III
D. Only I and III
E. All of the above

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Hello,
Greetings for the day!

This is a simple question which tests your knowledge on basic concepts of Speed, Time and Distance.
Speed = Distance / Time; hence, Distance = Speed x Time.

Now, let us look at the problem at hand. The speed of the first flight is given to be in between 600 mph and 800 mph. This flight takes 2.5 hours i.e. (5/2) hours to cover the distance D. Hence, we can say
D = Speed x (5/2).
If the speed is 600mph, then D could be 1500 miles and if the speed is 800 mph, then D could be 2000 miles. But, since the boundary values cannot be included, we can rule out statement I. Hence, options A, D and E can be eliminated.

The speed of the second flight is given to be in between 800 mph to 1000 mph. This flight takes 1.75 hours i.e. (7/4) hours to cover the distance D. Hence,
D = Speed x (7/4).
If the speed is 800 mph, then D could be 1400 miles and if the speed is 1000 mph, then D could be 1750 miles. Again, since the boundary values cannot be included, we can rule out statement III. Hence, options C can be eliminated.

Option B is left, which HAS to be the answer because it falls between the boundary conditions in both cases.

There we go, the correct answer option is B.

In a ‘could be’ question, the idea is always to make a statement true, once, so that it can qualify as an answer. At the same time, statement which are DEFINITELY false need to be identified as well so that they can be eliminated as we did with Statements I and II.

The trap in this question - We do not have information about whether the boundary values can be included or not. So, the trap laid here is to play on your inability to decide whether ‘Between’ should include the boundary conditions or not.

By default, when you see the word ‘Between’, the boundary values are to be excluded, unless stated otherwise.

In an official question of a similar nature, the question will specify explicitly whether the boundary values have to be included or not.

Hope this helps.
Cheers!
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great Q?

Fortunately make the correct approach.
Kudo to EgmatQuantExpert ... especialy Payal