The question is impossible to answer because we know nothing of how the number is generated, measured, etc. In order to do this we need to know something like a standard deviation or variance or something.

However, thereisa convention which, though not particularly realistic, that answers your question depending on what class you are in. I note that the number 4.7 has two significant digits. The convention is, when no other information is given, that the least significant digit has an uncertainty of . So I would say that 4.7 represents the interval between 4.6 and 4.8. Or in your notation:

(This convention essentially comes from the idea that the number measured comes from rounding: 4.7 could be generated by, say, 4.651 all the way up to, say, 4.749, which is an interval of about 1 in the least significant digit. However note that you could equally well use this argument to show that the number 4.7 represents the interval from 4.6 to 4.7.)

-Dan