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Juanita opens a savings account and deposits $500 into the account. She earns 1.5% interest on the account compounded annually. In function [tex]\( j \)[/tex], [tex]\( j(t) \)[/tex] represents the amount of money in her account [tex]\( t \)[/tex] years after opening the account.

Which statement best represents the domain of this function?

A. [tex]\( t \geq 500 \)[/tex]
B. The set of integers
C. [tex]\( t \geq 500 + 500 \cdot 1.5\% \)[/tex]
D. The set of whole numbers


Sagot :

To determine the best statement that represents the domain of the function [tex]\( j(t) \)[/tex], we need to understand what the domain represents in this context. The domain of a function is the set of all possible input values (in this case, the variable [tex]\( t \)[/tex]) for which the function is defined.

Juanita deposits $500 into a savings account that earns 1.5% interest annually, compounded once per year. The function [tex]\( j(t) \)[/tex] represents the amount of money in her account [tex]\( t \)[/tex] years after opening the account.

### Step-by-Step:

1. Understanding [tex]\( t \)[/tex]:
- [tex]\( t \)[/tex] represents the number of years after she has made the initial deposit.
- Since time cannot be negative, [tex]\( t \)[/tex] must be non-negative.
- Additionally, since interest is compounded annually, [tex]\( t \)[/tex] should be measured in whole years (0, 1, 2, etc.).

2. Constraints on [tex]\( t \)[/tex]:
- [tex]\( t \geq 0 \)[/tex] because she cannot have opened the account in negative time.
- [tex]\( t \)[/tex] should be a whole number because the compounding happens annually (we can't have fractional years for our input).

Now, let's analyze the given options:

1. [tex]\( t \geq 500 \)[/tex]:
- This is incorrect because it incorrectly implies [tex]\( t \)[/tex] needs to be at least 500 years, which doesn't make sense for the problem.

2. the set of integers:
- While positive integers could be part of the domain, this includes negative integers which do not make sense in this context because [tex]\( t \)[/tex] cannot be negative.

3. [tex]\( t \geq 500 + 500 \cdot 1.5 \%\)[/tex]:
- This suggests a specific starting value for [tex]\( t \)[/tex] that depends on the interest calculation, which is irrelevant to defining the valid input for [tex]\( t \)[/tex]. The function's domain isn't defined by the specific interest-based amount but by possible values of [tex]\( t \)[/tex].

4. the set of whole numbers:
- This is correct. It accurately states that [tex]\( t \)[/tex] must be 0 or any positive whole number (1, 2, 3, etc.).

### Conclusion:

The statement that best represents the domain of the function [tex]\( j(t) \)[/tex] is:

The set of whole numbers.

This means [tex]\( t \)[/tex] can be any non-negative integer (0, 1, 2, 3, ...).
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