Which numeric type conversion is better for simple math operation?

Question

I want to know which conversion is better (regarding performance/speed and precision/most less loss) for a simple math operation and what makes them different?

Example:

double double1 = integer1 / (5 * integer2);
var double2 = integer1 / (5.0 * integer2);
var double3 = integer1 / (5D * integer2);
var double4 = (double) integer1 / (5 * integer2);
var double5 = integer1 / (double) (5 * integer2);
var double6 = integer1 / ((double) 5 * integer2);
var double7 = integer1 / (5 * (double) integer2);
var double8 = Convert.ToDouble(integer1 / (5 * integer2));
var double9 = integer1 / Convert.ToDouble(5 * integer2);

Actually my question is about the conversion not the type itself.

Answer 1

EDIT

In response to your totally changed question:

The first line double double1 = integer1 / (5 * integer2); does an integer division, so don't do that.

Also the line var double8 = Convert.ToDouble(integer1 / (5 * integer2)); is doing integer division before converting the result to a double, so don't do that either.

Other than that, all the different approaches you list will end up calling the IL instruction Conv.R8 once for each line in your sample code.

The only real difference is that Convert.ToDouble() will make a method call to do so, so you should avoid that.

The results for every line other than double1 and double8 will be identical.

So you should probably go for the simplest: var double2 = integer1 / (5.0 * integer2);

In a more complicated situation, time your code to see if there's any differences.