Among a sample of diverse coins from an unfamiliar country, each face of any coin portrays one of four things: a jud...

shunhe on June 30, 2020

Hi @joaquin-acuna,

Thanks for the question! So let’s take a look at what’s going on the stimulus. We have these coins that can portray one of four things: a judge’s head, an explorer’s head, a building, or a tree. Now, we’re told that none of the coins have heads on both sides. In other words, if a coin has a head on one side, then it won’t have a head on the other. We can diagram this as
?H (heads) one side —> ~H on other

And also, we know that all the coins with a judge’s head on one side have a tree on the other. In other words, if a coin has a judge’s head on one side, it has a tree on the other. And so we can diagram this

JH (judge’s head) one side —> T (tree) on other

Now we’re asked what must be true about the coins in the sample based on the stimulus. Take a look at the contrapositive of the last sentence. That is

~T on other side —> ~JH on one side

In other words, if one of the sides of a coin isn’t a tree, then the other side isn’t going to be a judge’s head. And that makes sense, because if the other side of the coin was the judge’s head, then what would be on this side would have to be a tree. And we can see that this is what (D) tells us. If a coin has a building on one side (which is not a tree), then it won’t have a judge’s head on the other; in other words, no coins with a building on one side will have a judge on the other.

Hope this helps! Feel free to ask any other questions that you might have.