Question
The ratio of David's pens to Levi's pens at first was 3 : 7. After David gave Levi 12 pens, the ratio of David's pens to Levi's pens is 1 : 3. What was the number of pens they had altogether?
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The ratio of David's pens to Levi's pens at first was 3 : 7. After David gave Levi 12 pens, the ratio of David's pens to Levi's pens is 1 : 3. What was the number of pens they had altogether?