In any GMAT word problem, find the question and define it first. Don't worry if the rest doesn't make sense, part of the reason for that is that you don't know what the question is. Here, it is the perimeter of the table. Make a drawing for geometry problems---even if there is one as you want to add information---then you can see it. That will make you more precise. Then translate the given information into mathematical symbols and your drawing. Then, in a formula problem such as this, stick to the formula about like glue. The perimeter is the sum of the two long sides (200) plus the circumference of the two identical half circles with diameter 75 (approximately 234).
As for efficiency hints, when the question says estimate, believe it. So, especially here, use 22/7 for pi. Thus, ten and 5/7 times 22, 220 plus roughly 14, 234.
Remember that in many ways the math section is the verbal section. The GMAT treats the high school math as the moral equivalent of reading English---it is largely taken for granted rather than directly tested. The skills to build are those involving the word translation into symbols.
I hope that this was helpful and clear.
