Answer:
37 pieces are left for Carol to find.
Step-by-step explanation:
John, Mary and Carol are putting a puzzle together.
Puzzle has total = 100 pieces
John has found = 35 pieces
Mary has found = 28 pieces
Total pieces are found by John and Mary = 35 + 28 = 63 pieces
Now the remaining pieces are = 100 - 63 = 37 pieces
So 37 pieces are left in the puzzle for Carol to find.