If 30% of the network are malicious, how many nodes would an SPV need to connect to, to be sure? If we assume that 30% of the network is malicious and colluding together to trick an SPV client, by telling him wrong information.

How many random connections would the SPV client, need to connect to before the probability that he has only connected to malicious nodes is negligible?

In other words:

If we assume that the SPV does not know that 30% of the network is bad. What is the probability that he randomly connects to 5 bad nodes in a row?
Under the assumption that the total node count is large enough that we don't have to care about the reduction of the ratio by only connecting to nodes we haven't connected to, yet: 

The chance to connect to five bad nodes in a row is 0.35 = 0.00243 = 0.243%. AFAIK, many SPV nodes only connect to 4 nodes, though. The probability then is 0.81%.