Settlement of cash discount - calculated correctly?

The partial invoices were also calculated correctly:
1. €20,000 * 0.98 = €19,600
2. €36,000 * 0.98 = €35,280
3. €25,000 * 0.98 = €24,500
4. €30,000 * 0.98 = €29,400
already paid in total:
€111,000 * 0.98 = €108,780

final invoice:
€121,000 * 0.98 = €118,580
still to pay:
€118,580 - €108,780 = €9,800

or calculated differently with the gross amounts:
€121,000 - €111,000 = €10,000 still to pay gross, minus 2% discount that also results in:
€10,000 * 0.98 = €9,800

The calculation is quite simple thanks to the mathematical associative law. The invoice amount is always 100% of the sum to be paid, less 2% discount, so 98% of the invoice amount must be paid. Bieber0815 had already nicely explained that.

Percentage calculation is therefore apparently not necessarily everyone's cup of tea even in the year 2015 and among merchants ...

Why? It was perfectly recalculated from 102% down to 100%. So percentage calculation understood and implemented perfectly. :)

Only the general understanding of "Skonto" was not applied. If anything, then: "Word problems are still not everyone's thing in 2015." :)

I would just follow up. Maybe it was just a brain fart, e.g., because he usually always subtracts the 19% VAT from the gross prices and entered the same way into the calculator here. So it could be a simple mistake.