You are not correct, the right answer should be 5-2 square root symbol. I couldn't find out how to put one there.
No. Mike wrote the ratio as the amount of change to the new amount. He should have used the ratio of the amount of change to the original amount, which is 55
55/275
, or 20%.
There is no graph for us to see
21 and -4, because -4x21 = -84, and 21+-4 (– 4) = 17