# Can ≈ be used to express an arbitrarily rounded rational number?

Is it a formally acceptable use of ≈ to express a rational number rounded to an arbitrary number of significant digits?

For example, $\frac{4}{7}\approx0.57.$

If formally acceptable, is it expected?

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I see $\approx$ to mean close enough for the purpose at hand. Rounding rationals is one of many cases, $\sqrt 2 \approx 1.4$ is another, also earth population $\approx$ 7 billion. – Ross Millikan Jul 3 '12 at 20:43
Makes sense. Thanks very much. – Anon Jul 3 '12 at 20:49
Or, as I saw in a paper once, $3 \approx \infty$. (Ps. @Ross: Would you like to make that an answer so it can be accepted?) – Ilmari Karonen Jul 3 '12 at 21:25

I see $\approx$ to mean close enough for the purpose at hand. Rounding rationals is one of many cases, $\sqrt 2 \approx 1.414$ is another, also earth population $\approx 7$ billion. Some people will use $=$ for anything that comes out of a calculator, but $\sqrt 2 = 1.41421$ is discouraged here.

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Whenever I use an equal sign in the case of $\sqrt{2}=1.4142$, I would have my students indicate the degree of accuracy like so: $\sqrt{2}=1.4142 \text{ (to 4d.p.)}$. – azetina Jul 3 '12 at 23:17