有題數唔識呀!!唔該!!好急咖~~

每打原子筆的原價
= 27 / (1 - 55%)
= 27 / 45%
= 27 / (45/100)
= 27 * 100 / 45
= $60

每枝原子筆的售價
= 60 / 12 * 55%
= 5 * 55 / 100
= $2.75

假設原子筆每枝原價為$X

X * 12 * (1-0.55) = 27
X = 5

如你問的是原價, 就是$5, 問啟章買原子筆的價錢, 就是$5 * 0.55 = $2.75