7. Olivia has 20 euros. Each of her four sisters has 10 euros. How many euros does Olivia need to give to each of her sisters so that each of the five girls has the same amount of money?
A 2
B 4
C 5
D 8
E 10
7. A The total amount of the money the five girls have is $(20+4 \times 10)$ euros $=60$ euros. Therefore, if all five girls are to have the same amount, they need to have $(60 \div 5)$ euros $=12$ euros each. Since each of Olivia's sisters currently has 10 euros, Olivia would need to give each of them $(12-10)$ euros $=2$ euros.