If you divide 9/2 you receive 4.5. Tho when you divide 1/3 you get .33333 (repeated), so now you know that both the fractions do not correlate. Now the 'multiples' of 1/3 are 2/ 6, 3/9, 4/12, 5/15, 6/18, 7/21 and so on. If you do the 'multiples' of 2/9 you get 4/18, 6/27. The common factors are 4/18 and 6/18. So know you know that Sandy is using 2/18 (or 1/9) cups more of sugar.
I think the wording of the question is off, since 2/9 is less than 1/3. I think the question meant to say "she increases it by 2/9" thus making this an addition problem.
1/3+2/9 Dind the lcm of 3 and 9 and transform the fractions appropriately: 3/9+2/9 5/9
