During a trial, an attorney is planning to call to the stand to testify six different witnesses - T, V, W, X, Y and Z. She will call each witness exactly one time and the order in which she calls them is subject to the following conditions:
The fourth witness must be T.
W and Y must both be called before V.
X must be called before W.
If the attorney calls Z first, which of the following could be her fifth and sixth witnesses respectively ?

Options

A. T and X
B. V and W
C. X and V
D. Y and V

Answer

D

Explanation

Begin "lt" is used to indicate before because the number of the witness called earlier will be lower than that of a witness called later, e.g., if X is alled first and W is called third, `XltW` because `1 lt 3`. The initial conditions do not determine any particular order, except that T must be fourth.
There is one further conclusion: since `WltV` and `XltW,XltV`. This further conclusion is the basis for the correct answer to Question 21.If you miss this further conclusion, when you get to Question 21, the fact that you don.t find a correct answer will prompt you to return to the initial conditions to look for it and this will consume some precious extra minutes.
Enter the additional information on a diagram :
`{:("1 2 3 4 5 6"),("Z T"):}`
Now, look for further conclusions. We know that W, X and Y must be called before V, so V must be sixth:
`{:("1 2 3 4 5 6"),("Z T V"):}`
Since X must be called before W, there are three possible orders:

So, the fifth and sixth witnesses can only be Y and V or W and V, in that order.