**The ratio of the number of pencils to the number of erasers in a box was 2:3. When 42 pencils were added and 15 erasers were removed, the ratio of the number of pencils to erasers became 3:4. How many erasers were there left in the box?**

**Solution**

Before

--> Pencils 2 units, Erasers 3 units

After 42 pencils added and 15 erasers removed

--> Pencils 3 parts, Erasers 4 parts

3 parts --> 2 units + 42 (x3)*

4 parts --> 3 units - 15 (x2)*

*(x3) and (x2) to give an equal number of 6 units for both equations.

9 parts --> 6 units + 126

8 parts --> 6 units - 30

9 parts - 8 parts --> 126 - (-30)

1 part --> 156

4 parts --> 4 x 156 = 624

Answer: 624 erasers

Answer: 624 erasers

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