parameters in knapsack example

[Sam]

In the knapsack example the parameters are:

    NGEN = 100
    MU = 50
    LAMBDA = 100
    CXPB = 0.7
    MUTPB = 0.2

Why is the sum of the mutation and the crossover rate 0.90 rather than 1.0? what happens the other 10% of the time?

Thank you.

[François-Michel De Rainville]

The get cloned as is.