Attempted codeforces Div-2 Round 248 couldn't even solve a single problem :'( very sad though I managed to look at other people's solutions on the site and got the concepts, but still my rating will go haywire :(
So problem 1 was basically ad-hoc  :- Problem 1 here
algorithm to deal with it  :-
BEGIN
input n
for i in range (1,n)
     input temp
     if(temp==100)
        hundredcount++
    else
       twohundredcount++
   [end of loop]
if (hundredcount%2==1) [if hundred count is odd]
   print("NO")
else if(hundredcount==0 and  twohundredcount%2==1)[hundred count is zero and two hundred count is odd]
  print("NO")
else
  print("YES")
END