WTF is two decimal places?

[whethergirl]

Sorry, thicko alert, I really am terrible at maths.

DS homework (year 5) requests ds to measure items: "You must use the correct unit of measure and present the answer to two decimal places."

I'm assuming the 'correct unit of measure' is cm but how do you write out the two decimal places? For example, he measured a dvd case which was 19.5cm. So to present as two decimal places....would that be 19.50?
That doesn't sound right

yes that is right.

Two decimal places = two numbers after the dot.

Yes, 19.50cm.

If it is more, then you round it up or down.

Really? 19.50cm doesn't look right to me??

This doesn't specify what "decimal places" means but might be useful anyway

x post. Ok thank you

You had it right

So if it was 19.7cm, I would round that up to 20.00cm?

Yes you're right although it's a silly way to ask for cm to be written. 1dp would make a lot more sense!

19.7 to 2dp is 19.70 :)

Ok got it! Thank you. I've just never come across 19.70cm before but if that's what the very good looking teacher wants, that's what he gets.

19.999 would round up to 20.00

Thanks Stirrup, that makes sense. It's just that we're never going to be that precise with a tape measure, so I guess it just means we have to stick a zero at the end of each answer. Pointless really.

Maybe cm isn't the correct unit of measure? Could be m

Oh Build that's just what I was thinking. DS says he remembers measuring cm. But he says "You must use the correct unit of measure" so maybe it depends on what we're measuring?? Oh help please. DS really needs an early night and this has to be in tomorrow.

Yes, depends what you are measuring. But you can do it in lots of units. For example, if you are measuring a room it could be 235cm x 427cm. In metres, this is 2.35m x 4.37m (to 2dp). In centimetres, it would be 235.00cm x 437.00cm (to 2dp).

Year 5?

i would guess that the 'correct unit of measurement' means use cm, don't use pounds or grammes or hours or litres or square inches.

Meters would work better. 0.15m is 15cm.
I would just write everything in cm to 1dp as it would grate on me to put a zero on everything!

2dp is more precise. (Though admittedly not when you're using a tape measure to obtain the value, in cm)

1.5cm could be 1.45cm or 1.54cm.
1.50cm is 1.50cm (then possibly many other decimal places, but they're being ignored, because they're so small, anyhow, hence 2dp)

Ah yes ouryve that does make sense. Only thing is DS only remembers using cm at school. And doesn't recall doing 1.45cm (why 1.54cm?? don't get that bit) instead of 1.5cm.

We've just measured 3 items using silly cms with a zero plonked on the end and a couple of bigger items using metres even though ds doesn't think he's measured in metres before.