Four Saturdays a term I teach a group of primary school age children at http://www.dssfrome.co.uk/ and the other day we counted in 5s from 0 to 100. That should have been no problem and everything went well up to 50. We counted null, fünf, zehn.....fünfzig, fünfundfünfzig - and this is where the trouble started. I carried on, sechsundfünfig (56), siebenundfünfzig (57), achtundfünfzig (58) ... until one of the children spotted the mistake!
Oh dear, I made the classic mistake many English people make, forgetting to say the units first, then the tens. Of course it should have been sechzig (60), fünfundsechzig (65), siebzig (70), fünfundsiebzig (75), achtzig (80), fünfundachzig (85), neunzig (90), fünfundneunzig (95), hundert (100).