In the twenty-first-century world - despite the availability of calculators on smartphones and computers - we all frequently need to be able to think confidently about numbers. Whether you're discussing percentages in a business deal, weighing up interest rates with a financial adviser, or even discussing sports averages, doing a little mental arithmetic is very often the key to appearing smart while thinking on your feet. Yet many of us lack confidence with numbers - perhaps because we were put off mathematics at school and decided we were 'no good' at it. If you freeze with panic when you need to deal with figures, the overall quality of your thinking is likely to be compromised, and that could affect your performance at work, in job interviews, at college - and even socially. The good news is that a little practice is often all you need to blow away those 'mathematical cobwebs' and become adept at juggling numbers. You'll also benefit across the board, because doing relatively simple mental arithmetic as fast as you can has been shown to be a key way of firing your brain cells prior to a big task, and so makes a great mental warm-up. Numerical thinking is a must for the digital age, and these 50 puzzles will foster key skills in managing figures and building confidence with numbers.