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A graduating class has 236 students. Among them, 142 enrolled in algebra and 121 enrolled in chemistry. What is the greatest possible number of students who could have taken both algebra and chemistry?
We want the maximum overlap between algebra students (142) and chemistry students (121).
The overlap is maximized when every chemistry student also took algebra (since 121 < 142, this is possible).
Maximum overlap $= \min(142, 121) = \mathbf{121}$.
Check: if 121 students took both, then students taking at least one subject $= 142 + 121 - 121 = 142 \leq 236$. โ
So the greatest possible number is $121$.
In qualitative research, the concept of theoretical (or data) saturation refers to the point at which no new information or themes are emerging from additional data collection.
Why 'purposive sampling'? Qualitative researchers deliberately select participants based on specific characteristics relevant to the research question โ this is purposive (or purposeful) sampling.
Comparison of qualitative sampling methods:
| Method | Description |
|---|---|
| Purposive | Deliberate selection based on specific criteria |
| Snowball | Participants recruit other participants (used for hard-to-reach populations) |
| Theoretical | Sampling continues until saturation โ guided by emerging theory (Grounded Theory) |
Since the battery is disconnected, charge $Q$ is constant:
$Q = C_0 V_0 = 12 \times 10^{-12} \times 10 = 120\ \text{pC}$
Initial energy: $U_i = \frac{Q^2}{2C_0} = \frac{(120\times10^{-12})^2}{2\times12\times10^{-12}} = 600\ \text{pJ}$
New capacitance: $C = KC_0 = 6.5 \times 12 = 78\ \text{pF}$
Final energy: $U_f = \frac{Q^2}{2C} = \frac{(120)^2 \times 10^{-24}}{2\times78\times10^{-12}} \approx 92.3\ \text{pJ}$
Work done by capacitor on slab $= U_i - U_f = 600 - 92.3 \approx 508\ \text{pJ}$
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