📝 Show Your Working
Not a calculator. A calculator gives you the answer, which is the least interesting part. This shows you how to get there — the carrying, the borrowing and the remainders, written out the way you would write them.
The sum
Step—
Ones worth watching
How to Use It
- Going through it
- Next and Back take you one step at a time, or Play runs the whole thing. The arrow keys work too. The column being worked on is picked out, and the sentence underneath says exactly what is happening there.
- Carrying
- When a column adds up to more than nine you can only write one digit, so the tens go to the top of the next column along. Only ever a one — two digits and a carry cannot reach twenty.
- Borrowing
- When you cannot take the bottom digit from the top one, you take ten from next door: the 6 becomes 16 and the neighbour drops by one. Nothing is created or destroyed — the top line is still worth exactly what it was before, which is the whole reason the trick is allowed.
- Long multiplication
- Multiply by each digit of the second number in turn and write each answer on its own line. The line for the tens digit gets a nought on the end, because that digit is worth ten times what it looks like. Then add the lines up.
- The bus stop
- Dividing is the one you work from the left. Ask how many times it goes into each digit, write that on top, and carry whatever is left over in front of the next digit. If it will not go at all, carry the lot and take the next digit as well.
- Why no leading noughts
- 207 − 140 works out column by column as 067, but nobody writes 067 — so it writes 67. Unless the answer really is nought, and then the nought is written, because otherwise there would be no answer on the page.