This is a normal bank or building society savings account with a tax-free wrapper. Name the predator and the prey.n Answers by e-mail to: UKColumn fool or by post to: Motley Fool, 79 Baker Street, London W1M 1AJ.n Last week’s answer: QXL. E-mail UKColumn fool or post to Motley Fool, 79 Baker Street, London W1M 1AJ.FOOLISH TRIVIAThe first five correct answers out of the hat win a copy of `The Motley Fool UK Investment Guide’.Maybe Germany won’t buy our beef, but that didn’t stop a British company from stepping up its efforts to buy into Germany’s telecommunications market last week. How do I tell which is the best performer?BE, BreconThe Fool responds: what an index tracker fund tries to do is follow a stock market index closely: one way of doing that is to split the total fund among all the companies in the index, according to index weighting.

So the measure of good performance that you should be looking for is low tracking error. All index tracker suppliers should be able to furnish you with a figure. Low charges are essential, as charges can make a huge difference to returns. We’d choose a tracker that has no entry or exit charges and we would insist on an annual management charge of 1 per cent or less.n If we publish your question, you’ll win a copy of `The Motley Fool UK Investment Guide’. If a company can do that, it is going to have more cash going into its coffers to fund future development and expansion. So we have bought some BT shares for our Rule Shaker portfolio.We’ll be making more purchases soon, and we will keep you up to date on the progress of the portfolio.The Rule Shaker is a real money portfolio, searching for both Rule Makers and Rule Breakers, and we publish the details only for educational purposes. That education extends to ourselves too, and we are learning as we go along.

Our buying and selling decisions are not meant as tips, and you should not rush out and buy BT shares just because we have done so.Foolish investors never follow tips anyway, but always make their own decisions based on their own analysis.ASK THE FOOLI am interested in starting investing in an index tracker fund. His response was professional, and he talked about quality of service, but our Fool was sure he saw a satisfied smile on Sir Iain’s face, and couldn’t help imagining him thinking “because we can, my dear, because we can”.Fools like companies that can keep their margins high while expanding. That now gives BT a total of 41 out of 60, and gains the accolade of second tier Rule Maker. Second tier does not mean automatic qualification, but it certainly warrants serious consideration.One of our Fools reported seeing BT chairman Sir Iain Vallance being interviewed the morning of the results, and he was rather naively being asked the perennial question of why BT continues to keep its prices high. On the last full-year results, we scored BT zero points for sales growth, simply because there wasn’t any. But sales are looking good now, and so this time we score the full 2 points out of 2. “Surely all those others are taking sales away from BT,” we might think But BT’s sales are growing.