Iam a 3digit number that is less than 500. my ones digit is twice the hundreds digit. the sum of the three digits is 14. what number am i?

The three possible answers are 428, 356, and 284. All are less than 500, all have a units digit twice the hundreds digit, and all have 14 as a sum of digits.

Ooh fun

so xyz=number
z=2x
x+y+z=14
subsitute z=2x into x+y+z=14
x+y+(2x)=14
3x+y=14
number must be 3 digit and less thaan 500
since the tens digit's max is 9 then
z+x≥14-9
z=2x
3x≥5
x max=5 because 500 is max so 
x could be 2,3,4 so 

284
356
428
are the numbers

The equation is y=17(7)+600 and it equals 717