Penelope had some chocolate bars. She sold 20% of her chocolate bars and gave half of the remainder to her sister. After that, she bought 12 chocolate bars and had a total of 18 chocolate bars in the end. How many chocolate bars did Penelope have at first?
Percentage of chocolate bars that Penelope left after selling 205 of her chocolate bars
= 100% - 20%
= 80%

Fraction of chocolate bars that Penelope had left after giving to her sister
= ¹₂ x 80%
= ²₅

Number of chocolate bars that Penelope had left = 2 u

Number of chocolate bars that Penelope had in the end = 2 u + 12

2 u + 12 = 18
2 u = 18 - 12
2 u = 6

1 u = 6 ÷ 2 = 3

Total number of chocolate bars that Penelope had at first
= 5 u
= 5 x 3
= 15

Answer(s): 15