The experimental probability that it will rain on any given day in houston, texas is 3 out of 20 days. about how many days can residents predict rain out of 365 days?

What we have here is a problem of proportions. We're assuming that the probabilities - the ratio of rainy days to total days - are equal; 3 is to 20 as something (let's call it r for "rainy days") is to 365. Mathematically, that gives us this equality:



To solve for r, we can simply multiply either side of the equation by 365:



365 and 20 have the factor 5 in common, so we can use that to reduce the fraction to: 



So, the number of rainy days, if that pattern continued, would be around 54 3/4 days, or 55, rounded up to the nearest day.