First, the tens. Most are simply the unit + -zig — vierzig, fünfzig, achtzig, neunzig:

Number	German	Number	German
20	zwanzig	60	sechzig
30	dreißig	70	siebzig
40	vierzig	80	achtzig
50	fünfzig	90	neunzig

Four need a second look: zwanzig (not zweizig), dreißig (with ß), sechzig (sechs loses its s) and siebzig (sieben loses its -en). And 100 is hundert — or einhundert.

In between, German says the unit first, then und, then the ten — all as one word:

• 21 — einundzwanzig, literally one-and-twenty
• 35 — fünfunddreißig
• 48 — achtundvierzig
• 99 — neunundneunzig

English once did this too — think of the nursery rhyme's four-and-twenty blackbirds. Note that eins drops its s: einundzwanzig.