Run R --version
there's info about version on the first line.
Edit: If you ask this question then I bet that R is not running from any of these directories. Check $PATH env variable to get information where binaries are looked for and in which order.
Edit 2: Use type
shell command to find where binary for given command is stored, -a
for all paths, -f
for the hashed one (basically: most recently used).
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