# If O is selected for the first Sunday, which one of the following is a concerto that must also be selected?

Anna on January 4, 2020

Can someone please explain this problem?

I don't see how you can infer that Y must be selected

Replies

Anna on January 4, 2020

*that K must be selected

Skylar on January 5, 2020

@AnnaC, happy to help.

We are told that O is selected for the first Sunday.

Rule #4 states: J and O -> J - O. The contrapositive of this is: O - J -> NOT J or NOT O.
Basically, this means that if both J and O are selected, J must precede O. If O would precede J, then they cannot both be selected. In this scenario, we know O is selected and is in spot 1, which means it would be impossible for J to be earlier than O. Therefore, J cannot be selected in this scenario.

The game setup tells us that exactly two of Giuliani's three concertos will be selected. Since we just eliminated J as an option, this means that the remaining two of Giuliani's concertos - H and K - must be selected. So, we can accurately say that K must be selected if O is selected for the first Sunday.

Does that make sense? Please let us know if you have any other questions and best of luck with your studies!

on June 8, 2021

Why is N also not the right answer since we also need two of R's concertos?