"The intersection (∩) of a pair of sets (G and H) is a third set (I) composed by the elements that belong, at the same time, to both given sets."
According to this definition:
Given the sets:
G = {3, 7, 8, 9}
H = {2, 5, 7, 8}
The Intersection is:
G ∩ H = I = {7, 8}
:-)
"Two significant figures" means that a digit after the second one could actually be anything ... it wasn't measured. 'X' could be anything from 230 to 239. 'Y' could be anything from 400 to 409.
The greatest possible value of that fraction is. (239)/(409 squared) .
To find the percent, divide 9 by 27 to get a decimal, then multiply the decimal by 100 to get the percent:
9 / 27 = 0.333
0.333 x 100 = 33.3%