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?
How many pebbles did Shawn have after painting the red and blue pebbles? ** After painting the red and blue pebbles, Shawn had a remainder of 40 - 9 - 13 = <<40-9-13=18>>18 pebbles.
How many pebbles did Shawn paint yellow? ** He painted 18/3 = <<18/3=6>>6 pebbles yellow.
What is the difference between the number of blue and yellow pebbles? ** The difference between the number of blue and yellow pebbles is 13 - 6 = <<13-6=7>>7.
#### 7