Calculator Annie — Alexander McCall Smith

No matter how hard Annie tries, she just cannot do even the simplest sums. It's so embarrassing! When she goes to the shops, she can't work out how much money to hand the shopkeeper, and she always gets 0 for her maths homework. That is, until Annie goes to sleep with a calculator under her pillow, and something very strange happens. Overnight, Annie becomes a maths maestro capable of solving problems so fast it takes people's breath away. It impresses one world-renowned maths genius so much that he decides to put Annie's powers to the ultimate test. Will Annie be up to the mathematical challenge, or will she be at sixes and sevens and end up back at square one? Prepare yourself for this brain-teasing adventure ...