Special products
MathematicsHigh school
Expanding (a + b)², (a − b)² and (a + b)(a − b) without going back through distributivity.
Click a card to see its answer. Series no. 399191 — this page’s address gives these exact cards again.
Other series
MathematicsMiddle school
Arithmetic with signed numbers
Adding, subtracting and multiplying signed numbers, where the signs trip up the reflexes.
MathematicsMiddle school
Decimal form of simple fractions
Turning a simple fraction into its decimal form, in your head, without doing the division.
MathematicsMiddle school
Linear equations
Solving an equation of the form ax + b = c in your head, with a whole-number solution.
MathematicsMiddle school
Percentages of a number
Taking a simple percentage of a number, and recognising an increase or a decrease.
MathematicsHigh school
Powers of ten and scientific notation
Moving between scientific notation and decimal form, and back, without a calculator.
MathematicsHigh school
Special values on the unit circle
The cosines and sines of the special angles, from 0 to π, given without thinking.