As noted in the comboxes, thirty is proving to be an unlucky number for Nick Clegg.
Bearing this in mind, here are a couple of other questions interviewers might like to put to the Lib Dem leader:
At roughly what percentage did Lib Dem poll ratings peak during the last parliament?
According to your own party members, roughly how many Lib Dem seats are at risk to the Conservatives?
UPDATE
Here's another question:
According to Ipsos Mori what, roughly, is the Conservative Party's percentage lead over Labour?
