Dark figure

Posted by drfg2008 on May 25, 2016; 1:42pm
URL: http://spssx-discussion.165.s1.nabble.com/Dark-figure-tp5732237.html

Does anyone have a literary reference to the calculation of unknown cases / “Dark figure” or knows how to solve (if at all) the following problem or has any idea?

The following example:
Two real estate platforms publish houses that are for sale (sold homes). These two real estate  platforms are independent of each other and cover a very large share of homes sold in a country per year. However, it is not known exactly what percentage of the total market each of the platforms cover.

It is known:
A) The number of sold homes per year, which were offered on platform X ONLY.

B) The number of sold homes per year that were offered on platform Y ONLY.

C) The number of sold homes per year, that were offered on both platforms, X and Y.

Question: How many properties have been offered in a specific  year (including the properties that were not on platform X and Y)?
thx