Maths metric conversions

I was learning to convert measurements.

the thing I found hard was that the instructions that they gave you was unclear.

what is said was 1km= 1000m 1m = 100cm 1cm = 1000mm

I got confused because first it said 1cm = 1000mm when 1 cm is actually 10mm.

Second i didn't know how I was meant to figure out 3cm = ____km with what it told me.

But thankfully the answer sheet was on the other page.

So I looked at a random question which was 0.2m = _____km, changed it to 0.5m = ____km

and then googled it. the answer was 0.0005.

so I immediately came to a conclusion that I had to just add 3 zeros to the front of the number.

Because I had to change m into km and km = 1000m and that has 3 zeros.