If x, y, and z are positive integers such that 6xyz + 30xy + 18xz + 12yz + 10x + 17y + 5z =481, find x + y + z.
Given the equation 6xyz+30xy+18xz+12yz+10x+17y+5z=481, we want to find positive integer solutions for x, y, and z such that the equation holds.
Notice that all the terms on the left-hand side are divisible by 5, so let's divide the entire equation by 5:
5(2xyz+6xy+3xz+2yz)+2x+17y+z=96.
Now, we can see that the left-hand side is a sum of terms, each of which is divisible by 5, except for 2x, 17y, and z.
For the equation to hold, the left-hand side must be a multiple of 5, and that means 2x+17y+z must be a multiple of 5.
Looking at the possible values of 2x+17y+z, we notice that 2x+17y+z ranges from 2+17+1=20 (when x=1, y=1, z=1) to 2⋅6+17⋅2+6=56 (when x=6, y=2, z=6).
Since 20≤2x+17y+z≤56, and we want it to be a multiple of 5, the only possibility is 25 (which is the only multiple of 5 in that range).
So, we must have 2x+17y+z=25.
To find the positive integer solutions for x, y, and z that satisfy this equation, we can try different values for x, y, and z in a systematic way. Starting from x=1, we can substitute values for y and z that satisfy the equation 17y+z=25−2x.
We find that x=1, y=1, and z=7 satisfy the equation 2x+17y+z=25.
Therefore, x+y+z=1+1+7=9.
So, the value of x+y+z is 9.