ability of mental arithmetic的用法和样例：
- Conclusion Addition of Abacus Mental Arithmetic training children to listen to accelerate the process of mental...
- A man sitting next to Ford at the bar looked at the two men, looked at the six pints, did a swift burst of mental arithmetic, arrived at an answer he liked and grinned a stupid hopeful grin at them.
- He got the answer by mental arithmetic.
- He is good at mental arithmetic.