Shawn collected 40 plain pebbles. He painted 9 pebbles red and 13 pebbles blue. He then divided the remaining pebbles equally into 3 groups, and painted them purple, yellow, and green. What is the difference between the number of blue and yellow pebbles? Let's be accurate as possible.
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After painting the red and blue pebbles, Shawn had a remainder of 40 - 9 - 13 = 18 pebbles. He painted 18 / 3 = 6 pebbles yellow. The difference between the number of blue and yellow pebbles is 13 - 6 = 7.
The answer: 7.
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