5 coloured counters 2 red 3 not red are place in a bag. a trial consists of counter being taken out, noted and replaced 20 tirals occur how many ways can 0 red counters be pulled form bag

Answer 1

There are only 3 ways that 0 red counters can be pulled out of the bag in 20 trials:

1. Pulling out a not red counter 20 times
2. Pulling out a not red counter 19 times and a red counter 1 time
3. Pulling out a not red counter 18 times and a red counter 2 times