Answer:
7:11.
Step-by-step explanation:
Number of students eating lunch = 660
Number of students purchasing lunch = 420
The ratio of the number of students purchasing lunch to the total number of students eating lunch will be:
![420\colon660](https://img.qammunity.org/2023/formulas/mathematics/college/p7g7u5yvsfgl472mmv4rf5ji38xxrc19jj.png)
We reduce it to its simplest form.
![\begin{gathered} (420)/(10)\colon(660)/(10) \\ 42\colon66 \\ (42)/(6)\colon(66)/(6) \\ 7\colon11 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/wfiu4zizz4w1gnq03yrkasi0emfdvvkvz0.png)
The ratio in simplest form is 7:11.