Me: What’s 18+7?
Student: *reaches for calculator*
Me: *before student finishes punching it in* It’s 25
Student: How do you beat the calculator all the time?
Me: What do you have to steal from seven to get 18 to a multiple of 10?
Student: 2
Me: Yep, what are the numbers now?
Student: 20 + 5?
Me: Yes!
Student: Wow!
Me: Think about that the next time you see someone bashing common core on Facebook. Every single common core rant I’ve seen on facebook shows the ranter’s complete ignorance of the deeper workings of arithmetic.