Answer: he bought 5 green pencils
Step-by-step explanation:
Let x represent the number of green pencils that Dustin bought.
Dustin bought 9 pencils. The remainder of the pencils were purple. This means that the number of purple pencils that he bought is 9 - x
Some of the pencils were green and cost $0.90 each. The remainder of the pencils were purple and cost $0.65 each. If Dustin paid $7.10 for all of the pencils, it means that
0.9x + 0.65(9 - x) = 7.1
0.9x + 5.85 - 0.65x = 7.1
0.9x - 0.65x = 7.1 - 5.85
0.25x = 1.25
x = 1.25/0.25
x = 5
