double selection probability

42 Views Asked by At

enter image description here

What I think we need to use $n+r-1\choose{r-1}$ for the pair $x+y=100$ I tried something like this there are total 24 pairs whose sum is 100 and 49 total odd so first selection will be $49\choose24$

After that i am stumped what to do ?

Please help

1

There are 1 best solutions below

9
On

Hint:

Can you construct an example in which no two element sum is equal to $100$?

Can you construct a set with less than 26 elements with no two elements sum is equal to $100$?

Feel free to ask for more clarification :)