Number
Types of number, factors and multiples
Every whole number is built from primes, like a molecule from atoms. Writing numbers as products of primes makes highest common factors and lowest common multiples quick. Along the way you meet the families of numbers: integers, squares, cubes, rational and irrational numbers.
≈ 30 minFractions and decimals
To add or subtract fractions, give them a common denominator. To multiply, multiply tops and bottoms; to divide, flip the second fraction and multiply. Every fraction is a terminating or recurring decimal, and every recurring decimal can be turned back into a fraction.
≈ 30 minIndices and standard form
Multiply powers of the same base by adding indices, divide by subtracting, and raise a power to a power by multiplying. , , and is the th root. Standard form () writes huge and tiny numbers compactly.
≈ 30 minSurds
A surd is a root that can't be simplified to a whole number, like . Keep surds exact: pull out square factors (), collect like surds, and remove surds from denominators by multiplying top and bottom by the right surd or by the conjugate.
≈ 30 minEstimation and limits of accuracy
Round to significant figures or decimal places, and estimate answers by rounding every number to s.f. A measurement rounded to the nearest unit could really be up to half a unit either side: those are its bounds. For calculations, choose the bounds that make the answer biggest or smallest.
≈ 30 min