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Carmen, This question is ambiguous  did Tom get 1/3 of the original number or, as the word "then" suggests, 1/3 of what was left? In the first case, you would model the problem by the following equation, where the numbers in parenthesis refer to proportions of the original bag:
("1" is the original bagful, "1/2" the proportion of the bagful given to Tina, and "1/3" the proportion of the bagful given to Tom.)
(The first parenthesized expression represents what proportion of her marbles she did not give to Tina, and the second represents what proportion of those she did not give to Tom.) Now, here's the funny thing. Both of these seem to have answers  but only one is possible in the real world, where marbles cannot be divided. So we know which answer must be right! Which one? (Hint: in each case, how many marbles would Ann have after the first gift?) Good Hunting! RD  


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