At some point during the year 2021, a public health official said:

"There is currently a reduction in the rate at which COVID-19 is spreading in our community."

Suppose
𝐶
19
(
𝑡
)
is the number of people who have been infected with COVID-19 at time
𝑡
days (including those who have recovered).

Which (if any) derivative of
𝐶
19
(
𝑡
)
is negative?
[ Select ]
Both C'(t) and C''(t) are negative
Neither C'(t) nor C''(t) are negative
The first derivative C'(t) is negative
The second derivative C''(t) is negative

What (if anything) can be said about
𝐶
19
(
𝑡
)
?
[ Select ]
C(t) is negative
C(t) is neither increasing nor decreasing
C(t) is decreasing
C(t) is increasing

Question

At some point during the year 2021, a public health official said:

"There is currently a reduction in the rate at which COVID-19 is spreading in our community."

Suppose 
𝐶
19
(
𝑡
)
 is the number of people who have been infected with COVID-19 at time 
𝑡
  days (including those who have recovered).

Which (if any) derivative of 
𝐶
19
(
𝑡
)
  is negative? 
[ Select ]
Both C'(t) and C''(t) are negative
Neither C'(t) nor C''(t) are negative
The first derivative C'(t) is negative
The second derivative C''(t) is negative

What (if anything) can be said about  
𝐶
19
(
𝑡
)
 ? 
[ Select ]
C(t) is negative
C(t) is neither increasing nor decreasing
C(t) is decreasing
C(t) is increasing

BlackTom AI · Accepted Answer

Question restatement and options
- Topic: Interpreting trends in C19(t), the cumulative number of people infected with COVID-19 over time t.
- First prompt asks which derivative is negative given the description: a reduction in the rate at which COVID-19 is spreading.
- Second prompt asks what can be said about C19(t) given that description.

Analysis of the first dropdown options
- Option A: The second derivative C''(t) is negative
  This option asserts concavity downward of the infection count over time. When a public health official notes a reduction in the rate at which infections are spreading, that implies the rate of change of the infection count (C'(t)) is decreasing. A decreasing C'(t) corresponds to a negative C''(t). Therefore, this statement aligns with the interpretation of a slowing spread, even if the total number of cases is still rising.
- Option B: The first derivative C'(t) is negative
  If C'(t) were negative, the total number of infections would be decreasing. The scenario describes a reduction in the rate of spread, not necessarily a reversal to a decline. It is common for cumulative cases to still grow while the rate slows, so C'(t) being negative is not required and often not correct in this context.
- Option C: Both C'(t) and C''(t) are negative
  This would imply the infection count is decreasing and concave downward. The premise does not indicate a decrease in total infections; it describes a slowing rate. Thus, this combined claim is not supported by the given description.
- Option D: Neither C'(t) nor C''(t) are negative
  If neither derivative is negative, C'(t) could be zero or positive and C''(t) could be nonnegative. That would correspond to a constant rate or increasing rate of infection growth, which contradicts the stated reduction in the rate of spread. Therefore, this option misreads the situation.

Analysis of the second dropdown options
- Option 1: C(t) is negative
  C(t) counts the number of people infected (including recovered). A count cannot be negative in the real world, so this option is not plausible.
- Option 2: C(t) is neither increasing nor decreasing
  Saying C(t) is neither increasing nor decreasing would imply a constant value over time (C(t) constant). That contradicts the idea that infections are occurring, albeit at a slower rate, so this is unlikely given the context of ongoing spread.
- Option 3: C(t) is decreasing
  A decreasing C(t) would mean fewer total infections over time, which contradicts the interpretation of cumulative infections that accumulate over time. Unless there were negative new infections (which is not meaningful here), this is not compatible with the scenario.
- Option 4: C(t) is increasing
  Even if the rate (C'(t)) is decreasing, the cumulative number of infections C(t) is typically still increasing over time, because cases accumulate. As long as the daily new infections are nonzero or positive, C(t) grows, though the growth may slow down. This aligns with the described situation where the spread is slowing but not reversing.

Summary of reasoning (distinctive reasoning patterns across options)
- For C''(t) negative: the idea of a slowing rate corresponds to concavity downward, which is a natural interpretation of a decreasing rate of spread.
- For C'(t) negative: this would only hold if the total number of infections were shrinking, which the scenario does not assert; hence this is not a required consequence of a reduced rate.
- For both C'(t) and C''(t) negative: simultaneous negativity would imply a shrinking cumulative count, contrary to continued infections.
- For neither derivative negative: contradicts the stated reduction in the rate; one would expect at least a negative second derivative or a nonnegative first derivative depending on the exact dynamics.
- For C(t) negative: counts cannot be negative; this is unsound.
- For C(t) neither increasing nor decreasing: implies a flat count, which contradicts ongoing infections.
- For C(t) decreasing: incompatible with a cumulative count that by definition non-decreases over time in typical infection reporting.
- For C(t) increasing: consistent with ongoing accumulation of cases even if the rate of increase is slowing.

MAT135H5_F25_ALL SECTIONS 3.2 Preparation Check

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