0.5×0.8=0.4 is a mathematical stalk. When netizens posted 0.5×0.8=0.4 on the Internet, many netizens came to the answer 0.5×0.8=0.04 without thinking, thinking that 0.4 was wrong, and the ensuing mutual spitting would bring fire, but in fact 0.5×0.8=0.4 was correct.