Question

how can we decrease the rate of evaporation of water from a covered beaker

Answer 1

by increasing humidity in the cover

Answer 2

1. keep the water in a container with less surface area as possible. container that are deep or Narrow are best for this.
2. reduce the air flow over the water by positioning windbreaks .
3. a thin layer of oil also prevent evaporation.
I an not sure about this answer.