That is incorrect. As samwell pointed out, U decay involve step wise process involving alpha and beta negative decay. Each step has their own half lives.
Back in 02, I remeber it was necessary to remmeber the decay steps. But since then, syllabus has been amended, and you no longer need to remember it.
I've seen this diagram before (in fact we had to draw it from data), but I think what phillipa needs to know is how to write it as a simple equation. I know I have a booklet to do, as an assessment, and one of the questions is that it gives you the aforementioned table, then says "Write the equation for the change". I have no idea how to do this either.
Sorry for the double post, but I talked to my teacher. apparently, at least for me, you have to write out the ENTIRE series of equations. i.e. U235 --> Th234 + He, continuing until you get to the lead. It sucks, yeah.