By Danielle Kate Wroe To those who aren’t good at mental maths, the iPhone calculator is somewhat of a lifesaver – but did you know you’re probably using it wrong? If you need to quickly split a bill when you’re out for food with your mates, or work out how much discount you’ll be getting off that pair of trousers on ASOS, many rely heavily on the trusty app because it’s easy to reach (unlike the calculator you likely used in school) and easy to use. But there are features you may be missing out on. If you’re adding up everything you’ve eaten and drunk, for example, and accidentally type in th…