# Difference between revisions of "1999 AMC 8 Problems/Problem 18"

## Problem

At Stinky Fat Papa Middle School the 108 students who take the Fat Papa Test meet in the evening to talk about food and eat an average of two full size, double chocolate, and creamy cakes apiece. Walter and Gretel are baking Bonnie's Smelliest Bar Cookies this year. Their recipe, which makes a pan of 15 cakes, lists this items: $1\frac{1}{2}$ cups flour, $2$ eggs, $3$ tablespoons butter, $\frac{3}{4}$ cups sugar, and $1$ package of chocolate pounds. They will make only full recipes, not partial recipes.

They learn that a big concert is scheduled for the same night and attendance will be down 25%. How many recipes of cakes should they make for their smaller party?

$\text{(A)}\ 6 \qquad \text{(B)}\ 8 \qquad \text{(C)}\ 9 \qquad \text{(D)}\ 10 \qquad \text{(E)}\ 11$

## Solution

### Solution 1

If $108$ students eat $2$ cakes on average, there will need to be $108\cdot 2 = 216$ cakes. But with the smaller attendance, you will only need $100\% - 25\% = 75\%$ of these cakes, or $75\% \cdot 216 = 0.75\cdot 216 = 162$ cakes.

$162$ cakes requires $\frac{162}{15} = 10.8$ batches. However, since half-batches are forbidden, we must round up to get $\lceil \frac{162}{15} \rceil = 11$ batches, and the correct answer is $\boxed{E}$.

### Solution papa

If there were $108$ students before, with the $25\%$ of students missing, there will be $75\%$ of $108$ students left. This is $75\% \cdot 108 = 0.75 \cdot 108 = 81$ students. These students eat $81 \cdot 2 = 162$ cakes. Follow the logic of the second paragraph above to find that there needs to be $11$ batches, and the correct answer is $\boxed{E}$.