What number is bigger than 0.3 but is smaller than 0.4?

There are an infinite number of them.

Here are a few to get you started:

0.3000000001

0.3000000002

0.300000001

0.3000000011

0.31

0.32

0.33

0.34

0.341

0.349

0.35

0.36

0.37

0.38

0.385

0.386

0.387

0.388

0.389

0.3891

0.3899

0.39

0.399

0.3999

0.39991

0.39992

0.39993

0.39999

0.399991

0.399992

.

.

.

etc.