Trump said he had HEARD from some economists it was up to 32%; some economists say it’s as high as 42%.
Since they have everyone's SS Number they know exactly how many people have weekly withholdings from their pay check, so they know exactly how many people are working just subtract that number from the work pool and wallah, you have the real percentage.
“...and wallah, you have...”
I think the word you’re looking for is “voila!”