Which would add up to 82. According to a freshman guide to Harvards Mathematics Department there are two first-year math courses the hardest one being Math 55. Here is a famous prize problem that Sam Loyd issued in 1882 offering 1000 as a prize for the best answer showing how to arrange the seven figures and the eight dots 4567890.
Well in my opinion the toughest sum is this.
How about I tell you the first. This quiz has some solid math questions that you may find tough to answer in one go. You might need a pen and paper to do this. First take all the even natural numbers greater.