How many cards did she give her sister

 Sarah had 55 cards. She gave 20% of them to her sister, 25% of the remaining to her brother, the rest to her best friend. 

a)   How many cards did she give her sister?

10 điểm
A. 5 cards
B. 10 cards
C. 11 cards
D. 45 cards

b)   How many cards did she give her best friend?

10 điểm
A. 33 cards
B. 20 cards
C. 10 cards
D. 30 cards