Use of 成 / 乘 number quantifiers in Cantonese
成: one tenth; 10 per cent
乘: multiply; multiplication

一成熟：rare (10% cooked) 三成熟：medium rare (30% cooked) 五成熟：medium (50% cooked) 七成熟：medium well (70% cooked) 全熟：Well done (100% cooked)
It is always &quot;(X)成&quot;  for &quot;(X)/10&quot;
一成 = 1/10
三成 = 3/10
五成 = 5/10
七成 = 7/10
十成 = 10/10
十二成 = 12/10 (overdrive)