While we do number talks to start our math block, I like the idea of this type of problem as an additional warm up or closure:
Umm...close? But last time I checked, that wasn't how much I'd save!
It's important for students to be able to analyze the mistakes of others and critique their reasoning (math practice #3). Plus this provides a great "teachable moment" on the importance of checking your work and how math truly is all around us.