I have a question about sample sizes.

I have a data set in which I have following conditions:

1. Day 1: Total=3500, Fail=200;Fail%=6

2. Day 2: Total=6700, Fail=340, Fail%=5

3. Day 3: Total=1100, Fail=50; Fail%=5

4. Day 4: Total=500, Fail=17;Fail%=3

5. Day 5: Total=70, Fail=2;Fail%=3

Is there any way to know if Day 5 data can even be considered in this analysis since sample size is extremely small as compared to Day 1 sample size data (both pass and fails)?

Which statistics test to use for such problem?

Do I need more sample size on days 3,4 and 5 or can I just use the sample size which I have and say confidently that the Fail% decreases from Day 1 to Day 5?