Question

Mr. D'souza has bought four cars - Merc, Honda, Ford, Zen - as presents for his
sons' birthdays, all of which are next week. Given the following information, what
will each son get?
Alan will not get the Honda unless Barry gets the Merc and Denzil gets the Ford.
Barry will not get the Ford unless Carl gets the Zen and Alan gets the Merc.
Denzil will not get the Zen unless Alan gets the Honda and Barry gets the Merc.
Alan will not get the Merc unless Carl gets the Zen and Denzil gets the Ford.
Barry will not get the Merc unless Alan gets the Zen and Denzil gets the Ford.
Alan will not get the Zen unless Barry gets the Honda and Carl gets the Merc.
Carl will not get the Zen unless Barry gets the Honda and Alan gets the Ford.
Alan will not get the Ford unless Barry gets the Zen and Denzil gets the Honda.
Carl will not get the Merc unless Denzil gets the Honda.

Answer 1

Let's put given 9 information in a table. The person in Bold Font will not get the
corresponding car unless the persons in Normal Font get the corresponding cars.
Also, the person will Italics will get the remaining car.
Merc Honda Ford Zen
1 Barry Alan Denzil Carl
2 Alan Denzil Barry Carl
3 Barry Alan Carl Denzil
4 Alan Barry Denzil Carl
5 Barry Carl Denzil Alan
6 Carl Barry Denzil Alan
7 Denzil Barry Alan Carl
8 Carl Denzil Alan Barry
9 Carl Denzil ? ?
Now, let's assume that Alan gets the Merc. Then from (4), Barry gets the Honda,
Denzil gets the Ford and Carl gets the Zen. But from (7), Carl will not get the Zen
unless Barry gets the Honda and Alan gets the Ford. Thus, it contradicts the
original assumption. Hence, Alan will not get the Merc.
Let's assume that Alan gets the Honda. Then from (1), Barry gets the Merc,
Denzil gets the Ford and Carl gets the Zen. But from (5) or from (7), it contradicts
the original assumption. Hence, Alan will not get the Honda.
Let's assume that Alan gets the Ford. Then from (8), Carl gets the Merc, Denzil
gets the Ford and Barry gets the Zen - which does not contradict any of the
statement.
Similaly, you can assume that Alan gets the Zen. (which is contradictory to (9))
Hence, Alan gets the Ford, Barry gets the Zen, Carl gets the Merc and Denzil
gets the Honda.