Round off decimal value up to nearest 0.05 value?

I was reading How to round decimal value up to nearest 0.05 value?.

It mentions the following stuff.

   Math.ceiling(myValue * 20) / 20

How开发者_如何学C does this hack work ? I mean how did we arrive at this solution?

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1/20 is 0.05

1/100 is 0.01

If you want to round to 0.01, you multiply by 100, round and divide by 100. Similarly, to round to 0.05, you do the same, but with 20.

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There is no library function for rounding to 0.05, but there is one for rounding to 1.00: ceiling. That's almost (well, double isn't absolutely precise) the same as the formula that you pasted (20 * 0.05 = 1)

Did you try to substitute something for your formula and see what happens?

1.03 * 20 = 20.60
ceil(20.6) = 21
21/20 = 1.05

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it maps 0.05 to 1 (by multiplication) inside the Math.ceiling function and then maps the result back to 0.05 (by division)