Learning
Systems and tricks that make numbers easier to handle without a calculator.
Spørretimen Explained
School teaches you to work right to left, because that is how you write. In your head it is the other way round. A walk-through of the techniques for addition and subtraction – round and correct, fill up to the ten, shift between the numbers, and why you never need to borrow.
Division feels harder than the other operations, but it is the method that is the problem – not the sum. A walk-through of factorising, splitting, short division, the divisibility rules for 3, 4, 7, 8, 9 and 11, and what to do when it does not come out even.
Percentages are the arithmetic people use most and get wrong most. A walk-through of the techniques – ten per cent as the starting point, the trick of turning the sum around, VAT in both directions, per cent against percentage points, and why up and down by the same amount does not return you to the start.
How do you learn the times tables without memorising a hundred facts? A walk through a technique for every table from 1 to 10 – doubling, the five rule, the digit rule for nines and the square numbers – and the few facts that genuinely have to be practised.
A method for mental arithmetic in which the times tables are replaced by one short rule per digit. The whole Trachtenberg system walked through, with the rule and an example for every digit from 2 to 12 – and how to check the answer.
There are more subjects than there are episodes. Say what you would like to hear about, and we will know where to start.