Answer the following question, with explanation first.
Brittany, Alex, and Jamy all share 600 marbles divided between them in the ratio 3:5:7. If Brittany gives Alex half of her marbles, what's the total number of marbles that Alex has?

260
The total ratio representing the number of marbles is 3 + 5 + 7 = 15.

From the ratio, the fraction representing the number of marbles that Brittany has is 3 / 15, which is equal to 3 / 15 * 600 = 120 marbles.

Alex has 5 / 15 * 600 = 200 marbles.

If Brittany gives half of her marbles to Alex, Alex receives 1 / 2 * 120 = 60 marbles.

After receiving 60 marbles from Brittany, Alex has 200 + 60 = 260 marbles.

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The answer: 260