In this case 0.1 and 0.7 are by default double type.
As per OriginalGriff sir presentation so both of addition value will expect 7.9999999999999999 instead of 0.8.
For the solution I am really impressed
And one more solution can possible if we will use decimal type also
Where decimal numbers are exactly representable in binary floating point 0.1, For values which are more artefacts of nature which can't really be measured exactly anyway, float/double are more appropriate. For example, scientific data would usually be represented in this form. Here, the original values won't be "decimally accurate" to start with, so it's not important for the expected results to maintain the "decimal accuracy
Console.WriteLine((int)(((decimal)0.1 +(decimal) 0.7) * 10));