Question #367, If V is after X, Y will be before R.

[anais.salazar]

I diagrammed it this way. X-V --> Y-R. However, I don't understand how the correct answer is R-Y--> V-X.

[ohthatpatrick]

The correct answer was just the contrapositive of the way you originally wrote down the rule. The contrapositive is a different way of saying exactly the same thing.

You should get into the habit of writing contrapositives whenever you write a conditional statement.

(When you get good enough at doing so, you can either stop writing them - because you'll be able to 'think' them naturally - or you can keep writing them since it only takes 2 seconds to do so).

If I have a conditional that says:
If Bob goes, then Pam goes.

B --> P

the contrapositive is always
If NOT the 2nd thing, then NOT the 1st thing.

If Pam does NOT go, then Bob does NOT go.

~P --> ~B

So you correctly symbolized the original rule as
X - V --> Y - R

So our contrapositive is
If Y is NOT before R, then X is NOT before V

In ordering games, there's no reason to say
Y is NOT before R
when saying
R is before Y
is much easier/clearer.

So while we could write the contrapositive as
~(Y - R) --> ~(X - V)

it's easier and clearer to just flip the ordering when you're negating an ordering rule and get

R - Y --> V - X

Let me know if you still have any questions about this.