Question: powerset P(A), injection and subset

Let A = {a1, . . . , a10} be a set of 10 distinct positive two-digit integers (i.e., each ai
is at
least 10 and at most 99).
For each subset B ⊆ A let f(B) denote the sum of all elements in B. (If B = ∅, set
f(B) = 0.) Thus, f is a function from the power set P(A) of A to N. Prove that this
function is not injective.
 
Please Wait...