Note: Catch the number 1 first. 20 per person on average. If he doesn't get 20 at 1, then he must be 20 more or 20 less. So more or less peas will be taken away by others. On average, he must have caught more or less than 1. As a person, it is impossible to make such a choice. Then he must have chosen twenty.
Similarly, No.2 and No.3 will choose this way, otherwise, their chances of death will increase compared with those who choose later. For No.4, he chose only 40. If he doesn't choose 20, 4 and 5 will be executed, so 4 chooses 20, so 5 has no choice but the last 20. So they all choose 20.
Humanely speaking, no one will choose anything other than 20.