Given the mean of three numbers and the value of one of the numbers, is it possible to determine the values of the other two numbers? [closed]

Solution 1:

Taking the information you have given:${x+y+21\over 3}=23$ , thus $x+y=48$

but there are infinitely many solutions to this equation so no unique solutions. In the general case you have given, you end up with the sum of the 2 numbers being some value so you also end up with infinitely many solutions.