Arithmetic with signed numbers
MathematicsMiddle school
Adding, subtracting and multiplying signed numbers, where the signs trip up the reflexes.
Click a card to see its answer. Series no. 123494 — this page’s address gives these exact cards again.
Other series
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 products
Expanding (a + b)², (a − b)² and (a + b)(a − b) without going back through distributivity.
MathematicsHigh school
Special values on the unit circle
The cosines and sines of the special angles, from 0 to π, given without thinking.