Answer:
![f(n)=-0.10n^2+8n+200](https://img.qammunity.org/2020/formulas/mathematics/high-school/mawmbhf51gjsyr8n14jgcl1q5jnxdyxyib.png)
Explanation:
Let n represent number of new members and f(n) represent membership money.
We have been given that there are currently 20 members in the school's Ski Club. So when n new members join, the total number of members would be
.
Since for each new member recruited the dues for all members will be reduced by 10 cents, so new dues would be
.
The membership money would be number of total members times dues as:
![f(n)=(20+n)(10-0.10n)](https://img.qammunity.org/2020/formulas/mathematics/high-school/nsnu3mjxry3zw693d8bm6x6qdp0m0l2mgw.png)
Since we need our equation in standard form, so we will use FOIL to expand our equation as:
![f(n)=20(10)-20(0.10n)+n(10)-n(0.10n)](https://img.qammunity.org/2020/formulas/mathematics/high-school/qe39nc2t8xmc1vaz14b6m2pwuu7n05yypn.png)
![f(n)=200-2n+10n-0.10n^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/m4rdx5suj7kr8101jp1tqmlqloj0yk3z5b.png)
![f(n)=200+8n-0.10n^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/nz6xst49q14np8pfkd3fanarwd5d55h1gf.png)
![f(n)=-0.10n^2+8n+200](https://img.qammunity.org/2020/formulas/mathematics/high-school/mawmbhf51gjsyr8n14jgcl1q5jnxdyxyib.png)
Therefore, our required equation would be
.