What is the answer to this quadratic functions question?

Question

A computer can sort x objects in t seconds, as modeled by the function below

t = 0.003x ^ 2 + 0.001x

how many objects are required to keep the computer busy for exactly 7 seconds?

Puzzling · Accepted Answer

Plug in t = 7 and solve for x:
7 = 0.003x² + 0.001x

Let's multiply everything by 1000 to get rid of decimals:
7000 = 3x² + x

Get everything on one side:
3x² + x - 7000 = 0

Using the quadratic formula, we get
x = (-1 ± √84001)/6

We can ignore the negative result.
x = (-1 + √84001)/6

That's the exact answer. If you want a rational approximation:
x ≈ 48.138

But I don't see how you can work on a fraction of an item. If we round down we get 48 items.
t = 0.003(48²) + 0.001(48)
t = 6.96 seconds

If we round up to 49 items:
t = 0.003(49²) + 0.001(49)
t = 7.252 seconds

Answer:
The closest answer is 48 items, but that takes just under 7 seconds (not exactly).

By the way, if it takes 7 seconds to sort a measly 48 items, I'd say it's time to get a new computer. :)

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