Fast oral calculation can only be completed correctly and quickly after training. I suggest you practice with the software of "quick practice of oral calculation". After practicing with this software, you can generally reach 30 to 60 questions per minute in a short time. If it's 50 questions, if you practice quickly with software, it only takes 1 minute to complete. This software is a real person pronunciation, automatically generating questions, automatically grading, and can customize and practice any number range. So it can be several times faster than doing problems on paper. it wont hurt you to try it There are many download addresses on Baidu's website, and then you can download and install the latest version.