My Little Pony: Equestria Girls - Better Together (2017) : 1x24

Pinkie Pie picks up a magazine Rarity left behind on her beach chair and finds a "best friends" quiz inside, and she decides to take the quiz with Twilight. Unfortunately, they keep coming up with the wrong answers to questions such as "What is your best friend's favorite food?" and "What is your friend's biggest fear?", and they both score a zero. Unable to accept the idea of failing a test, Twilight decides to run her own equations to prove that she and Pinkie are best friends. After several hours of writing equations in the sand, Twilight finally comes up with the answer, but the ocean tide washes her equations away. Pinkie fears all of Twilight's work was for nothing, but Twilight tells her their friendship cannot be measured by numbers.