Let EIF be the set of all natural numbers ending in 5. That is, EIF = {5, 15, 25, 35, 45, 55, 65, 75,.}.

Describe a one-to-one correspondence between the set of natural numbers and the set of EIF.

N={1,2,3,4,5,6, ... }

ElF={5,15,25,35,45,55,65,75 ... }

so let natural numbers to be n, so

a) count the distance between the numbers

b) add or subtract extra values

10n-5 would be one to-one correspondence.