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Strange behavior of Round[x_, .1] -- I want Round[2.40, .1] to be 2.4

Elaine Kant, SciComp Inc.
Posted 11 years ago 
InputForm[Round[2.40, .1]]

returns 2.4000000000000004

why isn't it 2.4 ??

how can I get it to return 2.4, or more generally, how can I get numbers approximated to n decimal places?
And I mean how do I really change the value; I know I can use NumberForm to change what is printed.
POSTED BY: Elaine Kant
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Mathematica uses binary floating point representation for approximate numbers (i.e. numbers with a decimal point). That means that you can never exactly represent a rational number whose denominator is not a power of 2 with an approximate number.
POSTED BY: John Doty

Thanks, but NumberForm also only affects the print form.

I think this may actually do what I want! N[Rationalize[Round[2.40000004, .01]]]]

In[12]:= InputForm[N[Rationalize[Round[2.400004, .1]]]]

Out[12]//InputForm= 2.4
POSTED BY: Elaine Kant
POSTED BY: S M Blinder

but it still bugs me.

Then see this Table command not obeying limits related discussion, please. The value 2.4 as a rational number is 24/10. Everything else is subject to a number representation.
POSTED BY: Udo Krause
POSTED BY: Elaine Kant
POSTED BY: Elaine Kant
POSTED BY: Udo Krause
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