Calculations with fractions N2.2 Core Plenary What do you notice when you subtract two unit fractions that have prime number denominators? What happens when you add the two fractions? Give some examples to illustrate your answers. For example, Fraction puzzles were enjoyed by the Ancient Egyptians. Try to solve this one: One quarter of a number is added to one third of the number. The answer is 14. What is the number? Preamble The first activity will recap previous work on recognising prime numbers and the addition and subtraction of fractions, in the context of a simple number investigation. The second activity involves trial and improvement in the context of fractions of integers. Pupils could be invited to make up their own Ancient Egyptian problems and try them on friends (perhaps as a short homework task). Possible content Addition and subtraction of fractions, recognition of prime numbers, fractions of integers, informal trial and improvement. Resources None. Solution/Notes The result, put algebraically (which pupils will not do) is . The starting number is 24. Original Material © Cambridge University Press 2009 Original Material © Cambridge University Press 2009