The letter F prefix to your serial number indicates that your Marlin rifle was made in the year 1949.
By including the serial number in your question,we will be able to answer when your Marlin model 336 was produced.
With the serial number that you provided,your Marlin model 1893 rifle was made in the year 1899.
Your serial number indicates that your Marlin model 30A was made in the year 1979.
Your Marlin model 30AS was made in the year 1984.
Your Marlin model 336RC(regular Carbine) was made in the year 1966 with the 2 letter prefix of AB to your serial number.
The 336 began production in 1948. It can not be a 336 and made in 1917. Cross reference your serial number ... google Marlin Serial numbers and click on an applicable site.
The R prefix to your serial number indicates that your Marlin model 336 rifle was produced between 1957-1958.
Take the first two digits of your serial number, in your case 20 and subtract that from 100. Your gun was made in 1980. Skeeter
MSRP new was $447.00. The serial tells that it was made in 1995 (first 2 #'s minus 100). You could get between 340-400 if it is in PERFECT shape.
The way to find the year on Marlin rifles manufactured after 1972 is to take the first two digits and subtract them from 100. 100-11=89 so your rifle was made in 1989.
With the serial number provided,your Marlin .22cal rifle was made by Marlin in the year 1985.