It's hard to hit this gross rent multiplier in CA unless you go pretty far inland to areas with lots of empty, buildable land.

Some properties will earn more and some will earn less, but if you average $300/month/property, multiply that x 20 properties and that gives you $72K annually.

Whether you are talking about Gross Rent Multiplier or Cap Rates, these numbers are ratios based on price.So, Cap rate is income/value.GRM is Value or price/income.So if an income approach is used, the numbers used in the income approach should normally come from sales in the market.

According to http://livebaltimore.com/city-living-essentials/property-taxes/, Current (July 1, 2013 to June 30, 2014) tax rates:Baltimore City: $2.248 for every $100 of assessed property valueMaryland State: $0.112 for every $100 of assessed property valueSo, I'm terrible at math but it seems like I should be able to take an assessed property value, divide by 100, then multiply that times 2.36.But then when I calculate the taxes based on tax assessment, for example, in this listing: http://www.zillow.com/homedetails/322-E-33rd-St-Baltimore-MD-21218/36477903_zpid/, and trying a few years' worth of assessments and taxes, I get a number that is about $50-55 off.

I just don't know what rate to use.When considering for a rental the first number calculated is the gross rent multiplier.

I just wanted a bit of help if you may know is the Formula to offer the seller the same in every state, like for example is Arizona still multiply by (0.7) as you do in Virginia by chance? 

**READ ALL QUESTIONS MORE THAN ONCE be clear on what is being asked because you will be given A LOT of superfluous information and you will go into overload trying to plug everything in,*** Math questions       Draw a "T" on paper as soon as you sit down                                     On top of "T" write P (Part)                                      Lower left write R (Rate)                                      Lower right write W (Whole) UNDERSTAND what you are solving for.. plug in what information youre given and solve accordingly.Ex. if numbers are side by side multiply, if above and below TBar divide.KNOW how to compute HUD calculations for both Seller and BuyerKNOW types of estates and agencyGodspeed

It's like multiplying yourself 100 fold. 

And the criteria they use is self admittedly very focused ("They calculated the rental return for each county by multiplying the 2014 fair-market rent for a three-bedroom home by 12 (months) and then dividing that yearly total by median sales price for the county.")The other points that you touch on are most probably to be found on more specialized sites in reports that require the diligent investor to cast a wider net and delve deeper in order to filter out, absorb and deploy the underlying knowledge found in all those disparate sources.

Multiply by 60 if the park pays water + sewer, and by 70 if not.