Easy-looking math sum leaves people scratching their heads - can you remember the special rule?

A brain teaser shared online this week has left people stumped. Can you remember the special rule taught in math class to figure out the correct answer?
Philadelphia Tribune

For too many American kids, math isn’t adding up

Math scores in the U.S. have been so bad for so long that teachers could be forgiven for trying anything to improve them. Unfortunately, many of the strategies they’re using could be making things ...
TribLIVE.com

Editorial: For too many American kids, math isn’t adding up

Math scores in the U.S. have been so bad for so long that teachers could be forgiven for trying anything to improve them. Unfortunately, many of the strategies they’re using could be making things ...