The sum of the coefficient of all the terms in the expansion  of (2x-y+z)20 in which y do not appear at all while x appears in even powers and z appears in odd powers is -

coefficient of general term=20!p!q!r!=20!p!q!r!2pxpyqzrwhere p+q+r=20,q=0⇒p+r=20 (p is even and r is odd).  ⇒even + odd = even (not possible) ⇒ Coefficient of such power never occur ∴ coefficient is zero