Hi everyone, I got a question about the POFOD.
Q1: Implementing modules by two way. 1: 4 errors in 1000 test cases; 2: 6 errors in 1200 test cases.

I got the P1=4/1000=0.004 and the P2=6/1200=0.005. Is the method of P2 more reliable?

Q2: Now implement modules by 1, if 1 failed 2 will take over. What's the POFOD?

I got two answers for the POFOD.
1: P=P1 * P2=0.004*0.005=0.00002
2: P=1-((1-P1)*(1-P2))=1-((1-0.004)*(1-0.005))=1-(0.996*0.995)=1-0.99102=0.00898
I am confusing with the two answers, could any one tell me which one is correct?

Thanks in advance!