One nice way of solving this is trying cases. Since we want to know if A sent at least 10 representatives, we'll try both 9 reps and 10 reps and see if each case is possible. If each one works, then we know the statements are INSUFFICIENT; if only one works, then the statement(s) are SUFFICIENT.
Given S1, let's see if we can make A send exactly 9 reps. The conditions we have to observe are these: (i) A sends the second most reps; (ii) another country sends 41; (iii) each of the six countries sends a unique number of reps; (iv) 75 reps are sent in total.
If have the countries send 41, 9, 8, 7, 6, and 4 reps, respectively, we've observed all the conditions and we don't have A sending at least 10 reps.
On the other hand, the countries could send 41, 10, 8, 7, 6, and 3 reps, respectively.
So it's possible for A to send 9 reps or for A to send 10 reps, so S1 is INSUFFICIENT.
With S2 and with the two statements together we can use the exact same two cases we just used, as both will still be valid. Hence we don't know if A sent at least two reps, and the two statements together are INSUFFICIENT.
