Final answer:
The ratio of students who used a pen to those who did not is 20:12.
Step-by-step explanation:
The ratio of students who used a pen to those who did not is 20:12. To find this ratio, you divide the number of students who used a pen by the number of students who did not use a pen. In this case, 20 students used a pen and 32 students took the quiz in total, so 32 - 20 = 12 students used a pencil. Therefore, the ratio is 20:12.