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I'm trying to create a mathematical operation that help me to resolve this scenario.

I have a list of "limits" as show below:

0---4---8---12... (n + 4)

Suppose that we have a software that "read" a number, an it determines what is the previous "step limit". For example:

Given | Previous limit step
3     | 1 (the limit would be 0)
4     | 2 (the limit would be 4)
7     | 2 (the limit would be 4)
9     | 3 (the limit would be 8)

What I need to do is trying to get the previous limit in question, as show below:

Given | Previous limit
3     | 0
4     | 4
7     | 4
9     | 8

I have two days dealing with a formula to get it, but no good results.

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I feel so stupid.. viewing the results as table I think that the formula is limit = 4(n-1) – manix Oct 12 '12 at 18:16
up vote 1 down vote accepted

$x - (x \text{ mod } 4)$ should be what you are looking for. $\text{a mod b}$ returns the remainder of $a$ divided by $b$, i.e. what remains of $a$ if you subtract $b$ is many times as possible without making the result negative. In a of programming languages, operator "%" means $\text{mod}$, so you'd write x - (x % 4) to compute your "previous limit".

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You are correct – manix Oct 13 '12 at 6:07

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