The figure shows roads between two towns, A and B, in a mountainous area. During the winter, travel is difficult because of the threat of snow. The probability that any given road will be impassable in winter is '0.78. The conditions on the roads are independent. Find the probability that there will be a passable route from A to B. Roads can be travelled in either direction. A Roads between A and B 1 2 3 4 5 6 7 8 B