Solution:

1、

(1) It will take X days for Party B to complete this project alone.

20/(x+30)+20/x= 1

The solution is x=-20 or x=30.

It is verified that x=-20 or x=30 is the solution of the original equation, but x=-20 is not satisfactory and should be discarded.

∴x+30=60

Answer: It takes 60 days and 30 days for Team A and Team B to complete this project alone.

(2) (1-a/60) ÷ (1/60+1/30) = (20-a/3) days.

(3)

Set a to y days separately, according to the meaning of the question.

y+(20-y/3)×( 1+2.5)≤64

The solution is y≥48.

Answer: Team A should work alone for at least 48 days.

2、

The answer is as follows: