which three odd numbers from 1 to 17 add up to 30? i.e - + - + - =30
use 1,3,5,7,9,11,13,15,17
+118608 $$\\(2x+1)+(2y+1)+(2z+1)=30\\
2x+2y+2z+3=30\\
2(x+y+z)=27$$
If x and y and z are all integers there can be no answer to this.
Put more simply, If you add two odd numbers you get an even one. then
if you add on another odd number the answer must be odd. So it cannot be 30 
+118608 $$\\(2x+1)+(2y+1)+(2z+1)=30\\
2x+2y+2z+3=30\\
2(x+y+z)=27$$
If x and y and z are all integers there can be no answer to this.
Put more simply, If you add two odd numbers you get an even one. then
if you add on another odd number the answer must be odd. So it cannot be 30
