Question

A subset S of the set of integers 00, 01, ..., 99 is said to have property P if it is impossible
to find two numbers N1 & N2 belonging to set S such that unit digit of N1 and tenth place as
of N2 is same. Find the maximal numbers of elements in set S with property P
pls help .​

Answer 1

Hello, your answer is:
N2 is same so 1234567890