To OP, your fertilizer/seed guy probably meant to have a FINAL stand of 100,000, BUT most soybeans bags only mention about 90% germination, thus you have to "overplant" somewhat just to achieve 100,000 emerged, living soybean plants.

I plant 19" rows (have homemade interplant row units, on an 8 row wide JD planter = one pass), and at roughly 135,000 planted seeds, my monitor says 2.4 to 2.5" between seeds (thus I'm roughly "5 planted seeds" per 1 foot of a 19" row) Remember that not all of those seeds will grow, either.

I would try for 4 - 5 seeds, per foot, per each pass, then at 4 seeds(per 38" planter pass) will equal rough 110,000 seeds per acre(with two passes), and at 5 seeds per each 38" planter pass will equal roughly 137,500 seeds per acre (with two passes). Remember not all of those seeds germinated or make it out of the ground.

{Edit: After I reread the OP post, looks like the seed guy and I both recommend 4-5 seeds per foot, on each 38" planter pass}

This is from Iowa State University internet .pdf file:

How do you calculate plant population and seeding rate?

Plant population per acre is equal to:

[43,560 ÷ (row spacing in inches ÷ 12)] X plants per foot of row

Seeding rate per acre is equal to:

                    Suggested plants per foot of row                   
Percent germination X Percent expected emergence