Catching mice

[CMarangon]

Hello!

(50 secs reading text)


Problem:

There are 50 mice in a warehouse.
The owner of the warehouse hired a cat able to catch 80% of all mice.

How efficient is the cat, if it was put to catch mice,
first time in a saturday and other time a week after?

In HP50G:

Formula:
E = 1- (1- Eo)²
Where:
E, total efficiency
Eo, efficiency of the cat

Program:
≪CLEAR
"Enter Eo (cat efficace)" ""
INPUT OBJ→ → E0

≪
'1-(1-E0)^2' →NUM
≫
≫

I just want to know if I am using the correct formula.
Is it the correct fomula?

Original problem also asks how much mice remains alive after the second week.
But this is there just to test the formula.