what would you say, does the decimal point move or does the duodecimal point move?

]]>But intuitively moving the number to the left is best. That is because the decimal point is fixed, it separates non-negative powers of ten from negative ones.

]]>Wait! Remember the old style calculators with the LED ( red ) digits. If you put a number in there and multiply by 100, using a strobe light ( at a precise frequency of 1.2387 khz ) you can see the decimal point actually crawling to the right. Sort of like those old follow the bouncing ball sing alongs.

]]>I take the point (sic) about a fixed decimal position, but still feel that in practice we mentally move the decimal when multiplying by 10.

(bobbym: you can still look up to Mickey Rooney)

]]>What prompted that question? Do you know something?

Hi Bob;

The authority figures were anyone who was older than I. Since I was about 7 that meant the entire world was to be treated with respect. I agree, an outdated concept. Even I, the older I got there were obviously less people to treat that way. When I reached my present age, only George Burns and Bob Hope needed to be treated that way. Now they are dead...

]]>My preference is that the columns are fixed with the decimal point at the dividing line between whole numbers and decimals less than one.

So that means, for me, it is the numbers that move.

In the UK at primary level children are taught initially to put column headings: hundreds, tens and units and must keep columns vertically neat, so that adding etc works nicely.

If, say, you want to develop understanding of x ten you can then proceed like this.

eg 3 x 10. Put tens and units column headings. Enter a 3 in the units column. Then another underneath, then another and so on until you have ten of them. Add them up. Hopefully get 30. Enter this result with a 3 in the tens column and a zero in the units column. It seems basic but, if children follow these rules consistently, then doing 0.3 x 10 is just the same, except you put the .3s in the tenths column.

See picture.

Bob

ps.

authority figures like teachers

Who are they then?

]]>we too were taught to move the decimal point to the left by 2 places when you multiply by 100,but now when i'm thinking about it ,it may be more intuitive the the number moves to the left by two places.

]]>Never gave it any thought ( authority figures like teachers were obeyed then, hmmm ). We were taught to move the decimal 2 places to the right.

]]>And do you have reasons for your choice?

]]>