Question

two sisters together have 20 books. if the younger sister lost 3 books and the older sister doubled the number she has, they would have a total of 30 books. How many books does each have?

Answer 1

The older has 26 and the younger 4

Answer 2

Now:
older sister --- x
younger sister --- 20-x

new scenario:
older sister --- 2x
younger --- 20-x - 3 = 17-x

2x + 17-x = 30
x = 13

so now the older has 13, the younger has 7