For better or worse, this site is supported by advertisement. We are very selective about which advertisements are allowed and which are not. For example, besides having adopted a natural restriction to family ads, we do not display loop animation or popups. It does not mean that we like the ads that do get through. You - the visitor - do not have to, either. But sympathies apart, the ads slow down noticeably the loading of pages.

You may try an ad free browsing for short intervals of 1 day, 1 week, or 1 month. Upon receiving a payment (via one of the PayPal buttons below), a cookie is deposited at your computer that will expire in 1, 7, or 31 days depending on your choice. The upside of this arrangement is that no personal information is needed (nor collected). The downside is that this is a per computer arrangement. The cookie is left only once on the computer from which you accessed the PayPal site.

The site is worth browsing. It contains in the order of 4000 pages covering topics in arithmetic, algebra, geometry, probability, calculus, computer magic, visual illusions, and more. There are more than 970 interactive illustrations and a few dozens of math games and puzzles.

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