Key Maths is a series of graded activity books that reinforce children's mastery of important skills and concepts as required by the Primary National Strategy for maths at Key Stage 1. Areas covered include algebra, measures, money, fractions and data handling. Key Maths Book 4 includes: numbers to a hundred, tens and units, vertical addition and subtraction of 2-digit numbers, capacity (litres), counting in tens, quarter past and quarter to times, odd and even numbers and right angles.