A simple calculation problem A simple method to calculate the problem, I want to take off the formula Oh! 101 times 99 minus 199 thank you very much!

A simple calculation problem A simple method to calculate the problem, I want to take off the formula Oh! 101 times 99 minus 199 thank you very much!

101×99-199 =(100+1)×99-199 =99×100+99-199 =9900-100 =9800