I saw this quiz on Facebook. There is always stuff like this on Facebook.
There must have been at least 50 problems here. They are all multiple choice. The goal is to do them without a calculator. Most are on the 4th to 5th-grade level. I got them all correct.
They had one problem where they actually got the answer wrong, but since none of their choices matched the correct answer, I guessed correctly the incorrect answer.
The problem was "What is 411 - 401.1?". The correct answer is 9.9, but they listed the answer as 10.1.
They even said that the problem is tricky without a calculator.
The toughest problem was a single 2 digit by 2 digit multiply. I can do these in my head, but it takes effort.
My one difficulty is that I'm always looking for shortcuts to solve problems in my head when sometimes it is best to just stick to basic arithmetic.