A push-cart vendor is selling sodas at the beach. partway into the day, he raises his
price per bottle by one quarter. after this price increase, the total dollar amount
collected for the day after selling n bottles at the new price is given by the following
equation:
t = 12 + 1.75n
according to this equation, how many bottles did the vendor sell today before raising the
price?
o a
8
ob.
12
c. 18
d. 21

Notice that in equation for the total dollar amount collected ([tex]12+ 1.75\, n[/tex]), every additional bottle sold at the new price brings in [tex]1.75[/tex] dollars:

[tex]\begin{aligned}& 12 + 1.75\, n && \text{$n$ bottles at new price} \\ -\; & 12 + 1.75\, (n+1) && \text{$(n+1)$ bottles at new price} \\ =\; & 1.75\end{aligned}[/tex].

Therefore, the per-bottle price after the [tex]\$0.25[/tex] price increase would be [tex]\$1.75[/tex]. The per-bottle price before the price increase would be [tex]\$1.75 - \$0.25 = \$1.50[/tex].

Also notice that when [tex]n = 0[/tex], the total amount collected was [tex]t = 12 + 1.75\, n = 12[/tex]. In other words, the total amount collected was [tex]\$12[/tex] before any bottle was sold at the new price.

Thus, the vendor had collected [tex]\$12\![/tex] by selling at the initial price of [tex]\$1.50[/tex] per bottle. The number of bottles sold at that price would be:

[tex]\begin{aligned}\frac{12}{1.50} = 8\end{aligned}[/tex].