There is a question that really stumped me is (show in the picture)
At the beginning, I have no idea about figuring it out without calculator, and I just guessed the value of each number. √M is between √30 and √40, so the value must be around 6. And √N is between √3 and √4, so the value must be under 2 but more than 1. Then just plus 6 and 1.5 together the answer is C.