육십
yuksip · TOPIK 1
sixty
육십 = 육 (six, 六) + 십 (ten, 十): six tens make sixty
Sino-Korean numbers stack like multiplication: a digit placed before 십 (ten) multiplies it. 육 is six and 십 is ten, so 육십 is six tens. The same pattern gives 이십 (twenty), 삼십 (thirty) and 칠십 (seventy).