Conventional advice is that you do not want to apply more than one pound of nitrogen per thousand sq ft of lawn. Fertilizers are labeled with percentages of NPK that they contain. 20-10-10 means the bag has 20%N (nitrogen), 10% P (phosphorous) and 10% K (potasium). Dropping 5 lbs of product over 1000 sq ft would resultin 1 lb of N and 1/2 lb. ea. of P and K. As the rule is that you do not want to drop more than 1# of N, at a time, you can deduce that the testing facility is advising that you feed 1/2# each of P and K, and 1# of N.
Based on the above, you should be able to calculate what rate to drop any given fertilizer to achieve at least one of the NPK nutrients.
Many garden stores or nurseries or Lesco stores sell what is called triple NPKs, e.g. 10-10-10, 12-12-12 or 19-19-19 if you can't find exactly 20-10-10.
Ignoring enviormental issues and some debateable observations/arguements, adding up to a pound of P and/or K is not going to hurt the grass. Adding more than a pound of N can have adverse consequences. Point is, you can use a triple NPK at a drop rate of 1# of N per thousand sq ft (which would also be dropping 1# of P and K) without harm. or you could drop a tripple at half rate (1/2# of NPK per thousand sq ft.) and make up the other recommended 1/2# of N, by dropping 1/2N using Milorganite (organic), urea or any fertilizer (synthetic) labled X-0-0.

Don;t worry about 20-10-10 means nothing. Apply one application, of 10-10-10 which is a very common formula at a rate of 10-pounds of product per 1000/ft2. After that just use 39-0-0 rest of the year.

Your real problem which cannot be solved is the soil PH of 7.9. You are going to have to use an iron supplement to force feed iron to the grass.

Thank you guys for the replies.
I guess what confuses me is how much to apply per sq-ft.
My lawn is 5000 sq-ft, and assuming I'm using a 10-10-10 bag, does this mean I have to spread 50 pound total? And how often?

On a side note, the closest I found so far is the Scott's Green Max at 22-2-2 plus 5.75% iron. The bag is 18 pounds and they say it covers 5000. Do I have to apply 2 bags?

As for other bags, can you point out the exact bag, brand, store where I can find it?

Thanks again.

Thank you guys for the replies.
I guess what confuses me is how much to apply per sq-ft.
My lawn is 5000 sq-ft, and assuming I'm using a 10-10-10 bag, does this mean I have to spread 50 pound total? And how often?

On a side note, the closest I found so far is the Scott's Green Max at 22-2-2 plus 5.75% iron. The bag is 18 pounds and they say it covers 5000. Do I have to apply 2 bags?

As for other bags, can you point out the exact bag, brand, store where I can find it?

Thanks again.