6.4 and 6.40 equivalent or not equivalent?

yes because the 4 is in the tenths place and if you move the zero off 6.40 its the same as 6.4.Eg3.09 is equivalent to 3.090. Both of the nines are in the hundredths place.

Yes it is, just usually when theres zeros some people choose not to write them in, for example 6.4 is also equlivent to 6.4000000.......(infinate number of zeros) but no-one writes in all the zeros.

Yes (although the second implies a higher level of precision).

32/5

the equivallent of 64 percent is sixty-four hudreths