having used the internet before I can work out that
$this = $(this);
$this.html($this.html().replace(/\*/g, 'x').replace(/\/\/g, '÷'));
.replace('*', 'x').replace('/', '÷')
This works exactly as you described, so if you're having problems look somewhere else. You just wrote an incorrect regular expression and did not read into the errors :) Regular expressions have to be between / symbols and those do not need escaping under any circumstance.
....replace(/\//g, '÷').replace(/\*/g, 'x'); "5*4/2=10".replace(/\//, '÷').replace(/\*/, 'x'); // returns "5x4÷2=10"
In some cases using new RegExp objects would provide better readibility, but in your case that might be clunky.
"5*4/2=10".replace(new RegExp('/', 'g'), '÷').replace(new RegExp('\\*', 'g'), 'x');