In the office supply store, Brittany bought 17 pens of three kinds: ball pens, gel pens, and ink pens, which cost $0.05, $0.10 and $0.25 each. The total that Brittany paid was $2.05. If Brittany bought twice as many gel pens as ink pens, how many ball pens did she buy?
Answers:
A) 4	B) 5	C) 7	D) 8	E) 10
Denote each pen with the first letter of its kind and build a system of equations:   55+10G+25I=205   5+G+I=17   G=2I   5+9I=41   5+3I=17   6I=24   I=4   5=5   Answer: 5   _____________
<result>B</result>
In the office supply store, Brittany bought 17 pens of three kinds: ball pens, gel pens, and ink pens, which cost $0.05, $0.10 and $0.25 each. The total that Brittany paid was $2.05. If Brittany bought twice as many gel pens as ink pens, how many ball pens did she buy?