20 - sumul (스물)

30 - surun (서른)

40 - mahun (마흔)

50 - shwin (쉰)

60 - yesun (예순)

70 - ilhun (일흔)

80 - yodun (여든)

90 - ahun (아흔)

100 - bek (백)

One thing I want to point out is that numbers ending in 1, 2, 3, or 4 will be shortened when a counter follows the number. For example, 11 cars will be yol han de (열한 대) instead of yol hana de.

Here are the shortened forms:

hana (하나) = han (한)

dul (둘) = du (두)

set (셋) = se (세)

net (넷) = ne (네)