x,y and z are positive integers such that x<y,x+y=201,z−x=200. What is the maximum value of x+y+z?

since z=x+200, maximum x will provide maximum z.

x+y=201, so x=200,y=1 provides maximum x.
But, x<y, so maximum allowed x is 100.

So, 100+101+300=501 is the maximum sum