Need assistance with this hw prob:

A communication network has 5 links (see attach.)

The prob. that each link is working is 0.9. What is the prob of being able to transmit a message from point A to point B.

My attempt was to say, that the prob. of transmitting (TX) a message is the prob. of the top series link + prob. of middle + prob. of bottom - prob. of all 3. That is,

$\displaystyle Pr(TX) = 0.9*0.9 + 0.9 + 0.9*0.9 - (0.9)^5$

But that is > 1. Doh.