I can't really help you with the number line because i can't draw it out but;
If you choose
16.45 , 16.42 and 16.47
Then you know that 16.45 will go exactly in the middle of the 16.4 and 16.5
For the rest, you could always try and measure out how much space is in between for exmple it could be 1mm for every 0.01?
It says estimate though so as long as you have an accurate guess i don't think it matters if you are slightly out.
Hope this helps a bit and sorry i couldn't be more of a help!
