I have grown a bit tired of engageNY videos and those that insist Common Core math is somehow superior to “old math.” Math is math. Look at the traditional example they always give to knock “old math.”
In order to understand this problem, one needs to have a firm grasp on place value. Place value is taught in kindergarten on up.
243 is 200+40+3
Many want to pretend that we simply taught children to cross out and adjust numbers because that’s what the algorithm decided- BS.
The foundation for this problem was previously laid down in K, built on in 1st, and practiced in 2nd grade and up. An algorithm would take seconds to teach, the “why” takes years- and before Common Core it did take years.
In fact, the groundwork was laid through hands on manipulative blocks.
I.e. 18-9. Students would physically manipulate the 18 from 1 ten and 8 ones into 18 ones before performing the operation. Why? Because you can’t take 9 ones away from 8 ones. Sounds like a pretty solid understanding and building of a number sense to me.
What we are now dealing with are highly decorated college profs that somehow believe they have become masters of math- mostly because teachers wanted to give it a chance.
The trial is over. Common Core math does little more than dilute the great work that we were doing before. Stop pretending this math was delivered from a mountain. It came from those with not an ounce of understanding about child development and their expertise in 3rd grade was granted because 20-30 years ago they were once 3rd graders.
Why can you solve this problem is a question that was asked and thoroughly answered long before Common Core.