To expand on Craig’s explanation:

You need to know the total weight of flour you use. If you would like 3 parts AP to 1 part Whole Wheat, your mix is 75% - 25%, but your total flour mix = 100%. You need to choose how much total flour you want to use. Let’s say 1,000 grams. 1,000 x 75% = 750g AP and 1,000 x 25% = 250g Whole Wheat.

Total Flour = 750g + 250g = 1,000g

Flour always adds up to 100%. In this case we have 75% AP + 25% Whole Wheat =100%

If you prefer to solve/think in words instead of numbers to get started, ask yourself “Compared to flour (which is always 100%) how mich of each of the following do I want to use: water, salt, oil (if any)and sugar (if any).

Using Craig’s percentages:

Water = 65%, therefore you need 1,000g x 0.65 = 650g water

Salt = 2.0%, therefore you need 1,000g x 0.02 = 20g salt

ADY = 0.6% therefore you need 1,000g x 0.006 = 6g ADY

This will make a batch lf dough weighing 1,676 grams. From there, you can easily scale this up or down.

Some people decide how much dough they want to wnd up with, then figure it backwards for each ingredient. To do this, choose the total dough weight you want to make, say 2,200 grams.

Make a small table like this

Total dough weight = 2,200g

Then add up the percents of each ingredient here, this will help you find your total flour weight:

Percents

100 flour

65 water

2 salt

0.6 ADY

167.6 is the sum of the percents

Then take total dough weight and divide by the decimal representing total percent for all ingredients. 167.6% = 1.676

2,200 / 1.676 = 1,312.65g total flour needed

From there, start with the now known flour weight and multiply by the bakers percentage already determined to figure out how much of each you need:

Flour 100% = 1,312.65g

Water 65% = 1,312.65 x 0.65 = 853.22g

Salt 2% = 1,312.65 x 0.02 = 26.25g

ADY 0.6% = 1,312.65 = 7.9g

Check sum of weights and percents

Percents: 100+65+2.0+0.6 = 167.6 OK

Weights: 1,312.65+853.22+26.25+7.9 = 2,200.02 OK

Edit: I had 10,000g flour on one line instead of 1,000. Fixed.