After five days, Chantel has 5 * 2 = 10 bracelets. Then she has 10 - 3 = 7 bracelets. After the next four days, she makes 4 * 3 = 12 bracelets. In the end, Chantel has 7 + 12 - 6 = 13 bracelets.
The answer: 13
Reverse engineering the question: For 5 days, Chantel makes 2 friendship bracelets every day. She gives away 3 bracelets to her friends at school. Then for four days, she makes 3 friendship bracelets every day. Then she gives away 6 bracelets to her friends at soccer practice. How many bracelets does Chantel have in the end?

We know that the top level just has one case. Since each level has one more case per side than the level above it, the second level has sides that are 2 cases long. We can figure out how many cases we need for the second level by finding the area of a square with a side length of 2: 2 cases * 2 cases = 4 cases. The third level has three cases per side, so we need to find the area of a square with side length 3: 3 cases * 3 cases = 9 cases. The fourth level has a side length of 4, so we find its area with 4 cases * 4 cases = 16 cases. Finally, we add up the number of cases we need on each level: 1 cases + 4 cases + 9 cases + 16 cases = 30 cases.
The answer: 30
Reverse engineering the question: Mark wants to build a pyramid of soda cases that's four levels tall. Each level of the pyramid has a square base where each side is one case longer than the level above it. The top level is just one case. How many cases of soda does Mark need?

The bird wants 12 * 6 = 72 twigs to add to the nest. It knows a tree that has dropped 72 * 1 / 3 = 24 twigs. Thus, the bird will still need 72 - 24 = 48 twigs to finish the nest.
The answer: 48
Reverse engineering the question: A bird is building a nest from twigs. The bird has put twelve twigs together already to make a circle. For each twig it placed into the circle, it wants to weave in six more twigs to fill out the nest. It knows a tree that has dropped a third of the twigs it needs. How many twigs will the bird still need to find to finish its nest?

After 30 days, there will be enough food left to sustain 300 people for 90 days – 30 days = 60 days. After the 100 people leave, there will be 300 - 100 = 200 people left. The 200 people will eat 200 / 300 = 2 / 3 as much food as the original group of people in the castle. The 60 days' worth of food will last this smaller group for 60 days / (2 / 3) = 90 more days.
The answer: 90
Reverse engineering the question:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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There are enough provisions in a castle to feed 300 people for 90 days. After 30 days, 100 people leave the castle. How many more days are left until all the food runs out?