So- 1

- 1 & lt； 2a- 1 & lt； 1

Get a-1; 1 and 0

A<2 and a>0 and 0

So 0

Because f(x) is a decreasing function, f (1-a)

So1-a >; 2a- 1

Get 3a

That is, a < 2/3

To sum up, 0 < a & lt2/3

My answer is also (0, 2/3).