Get the missing number in average

[intercooler]

Hi, is there a way to find the missing number from a set of numbers (2 in my case) that forms a given average.
e.g. i have average value 10, one of the numbers is 4 and the function should return 6, if i have a number 3, the function should return 7 etc.
Thanks

[daffodil11]

The average of 4 and 6 is not 10. If your average value is 10, and one number is 4, then the other number is 16.

(4 + 16) / 2 = 10

(4+x) /2 = 10

4+x = 10 x 2

4 + x = 20

x = 16

(Average * Count of Numbers) - Known Numbers = Missing Number

[intercooler]

wow, apologies for my math, i spent so much time trying to figure out how should i do it with a function that i totally blurred.
Many many thamks