The number of pens she bought is 30.
The first step is to determine the number of pens she has.
Number of pens she has = 20% x 100
= 0.2 x 100 = 20
The second step is to determine the number of pens she bought. This equation can be used to determine the answer:
(x - 20) / 20 = 0.5
Where x is the number of pens she bought.
x - 20 = (0.5 x 20)
x - 20 = 10
x = 20 + 10
x = 30
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