Why '5+5+5=15' is wrong under Common Core
Here's a "repeated addition" Common Core problem that's taught in third-grade in US schools.
Use the repeated-addition strategy to solve 5x3. If you answer the question with 5+5+5=15, you would be wrong. The correct answer is 3+3+3+3+3.
Mathematically, both are correct, but under Common Core, you're supposed to read 5x3 as "five groups of three." So "three groups of five" is wrong.
According to Common Core defenders, this method will be useful when students do more advanced math. This way of reading things, for instance, can be used when students learn matrices in multivariable calculus in high school.
But parents aren't happy about it.
Story by Jacob Shamsian and editing by Ben Nigh.Why 5+5+5=15 is wrong under Common Core - Business Insider:
