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Perry buys a bag of 20 carrots on the first day. The second day, he eats half of the bag. Each day after, he eats half of what is left in the bag. Create a sequence formula that describes the number of carrots Perry will have on any given day.

1 answer

Let's break down Perry's carrot consumption day by day.

  1. Day 1: Perry starts with 20 carrots.
  2. Day 2: He eats half of the 20 carrots, so he eats 10 and has \(20 - 10 = 10\) left.
  3. Day 3: He eats half of the 10 carrots, so he eats 5 and has \(10 - 5 = 5\) left.
  4. Day 4: He eats half of the 5 carrots, so he eats 2.5 (in practical terms, this means he might end up with 2 or 3, but we can use decimals for the formula) and has \(5 - 2.5 = 2.5\) left.
  5. Day 5: He eats half of 2.5, which is 1.25, and has \(2.5 - 1.25 = 1.25\) left.
  6. Continuing this process, we see that each day he eats half of what is remaining.

To express this mathematically, we can define a sequence where the number of carrots left on day \(n\) can be represented with the following formula:

  • Let \(C(n)\) be the number of carrots left on day \(n\).
  • The initial count on day 1 (when \( n = 1 \)) is \(C(1) = 20\).
  • Each subsequent day, the number of carrots left is half of what was left the previous day: \[ C(n) = \frac{C(n-1)}{2} \]

Using this recursive definition, we can express the number of carrots on any given day \(n\): \[ C(n) = 20 \times \left(\frac{1}{2}\right)^{n-1} \]

This formula shows that the number of carrots left on day \(n\) is equal to the initial number of carrots (20) multiplied by \(\frac{1}{2}\) raised to the power of \(n-1\).

Thus, the complete sequence formula describing the number of carrots Perry will have on any given day \(n\) is: \[ C(n) = 20 \times \left(\frac{1}{2}\right)^{n-1} \]