Madeeasy Testseries CN Q4

Question

Here why can’t the answer be  p1(1-b1)^L (1-p2)(1-p3) + (1-p1)(p2)(1-b2)^L(1-p3) + (1-p1)(1-p2)(p3)(1-b3)^L  ?

Answer 1

If you will take certain link then why you will think about other link error probability. suppose you take link L1 : P(L1)*NO bit error probability then why i will think about other link if already i have taken link L1