| Subject: | QA, Mental arithmetic |
| Format: | Electronic text |
| Date issued: | 2021 |
| Language: | English |
| Publisher: | Project Gutenberg, |
| Rights: | Public domain in the USA. |
| Download link: | How to become a lightning calculator [electronic resource] / Anonymous |
| Subject: | QA, Mental arithmetic |
| Format: | Electronic text |
| Date issued: | 2021 |
| Language: | English |
| Publisher: | Project Gutenberg, |
| Rights: | Public domain in the USA. |
| Download link: | How to become a lightning calculator [electronic resource] / Anonymous |