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Table[StringForm["p=`1`", i], {i, 0.05, 0.5, 0.05}]
  {p=0.05`, p=0.1`, p=0.15000000000000002`, p=0.2`, p=0.25`, p=0. 30000000000000004`, 
   p=0.35000000000000003`, p=0.4`, p=0.45`, p=0.5`}

Why do the results show small deviations from the expected numbers {..., 0.15, ..., 0.30, ...}?

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I (kind of) translated your question this time. But the site's language is English. – Dr. belisarius Jun 29 '13 at 3:13
Thanks for translated it – Matematicoaficionado Jun 29 '13 at 3:17
I believe the fundamental reason is that with fixed precision, floating point arithmetic -- on a machine that has to translate into binary and then back into decimal -- you get machine representational error of 1/10 and then: 0.05 + 0.05 + 0.05 // FullForm gives 0.15000000000000002. – murray Jun 29 '13 at 3:21
Table[StringForm["p=1`", N@i], {i, 5/100, 5/10, 5/100}]? – Dr. belisarius Jun 29 '13 at 3:35
This tutorial, which is part of overview of numbers and their forms, might be helpful explaining the ` and the representation of numbers. This tutorial explains further output formats. – Michael E2 Jun 29 '13 at 15:36

I think what you are looking for may be

Table["p=" <> ToString @ NumberForm[i, 2], {i, 0.05, 0.5, 0.05}]

{"p=0.05", "p=0.1", "p=0.15", "p=0.2", "p=0.25", "p=0.3", "p=0.35", "p=0.4", "p=0.45", "p=0.5"}

This is the simplest way I can think of that produces output with numbers formatted in the way you request.

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