B737SFP: That would have been mind-exploding for most of the cadets I've had through TR's in the past 15 years. Ask them questions like that and the first thing that is brought out is their Japanese brain. Simple mental arithmetic skills seem to have disappeared.
What I found missing on the line was the appreciation of quick 'gross error' checks. This could be load sheets, flight profile, sector fuel required, etc. Perhaps, one is they were never taught, and two is they require mental sums.