Final answer:
Cooper can decorate 9 cookies in 30 minutes.
Step-by-step explanation:
To determine how many cookies Cooper can decorate in 30 minutes, we need to find the number of cookies he can decorate in 1 minute and then multiply that by 30. We are given that Cooper can decorate 3 cookies in 10 minutes. So, in 1 minute, he can decorate 3/10 cookies. Therefore, in 30 minutes, he can decorate (3/10) * 30 = 9 cookies.