Number of one-one function from {a,b,c,d} to set {1,2,3,4,5} is 5P4=120n(s). The required possible set of value (f(a), f(b),f(c),f(d)) such that f(a)+2f(b)−f(c)=f(d) are (5,3,2,1),(5,1,2,3),(4,1,3,5),(3,1,4,5),(5,4,3,2) and (3,4,5,2) ∴n(E)=6 ∴ Required probability =