In Ngamongo village, a piece of work can be completed by 45 workers in 10 days. They worked for 4 days after which 15 workers were laid off. How many days could it take the remaining workers to comple

Total work = Number of workers $\times$ Total days

$$\text{Total work} = 45 \text{ workers} \times 10 \text{ days} = 450 \text{ worker-days}$$

Work done = Number of workers $\times$ Days worked

$$\text{Work done} = 45 \text{ workers} \times 4 \text{ days} = 180 \text{ worker-days}$$

Remaining work = Total work - Work done

$$\text{Remaining work} = 450 \text{ worker-days} - 180 \text{ worker-days} = 270 \text{ worker-days}$$

Workers laid off = 15
Remaining workers = Original workers - Workers laid off

$$\text{Remaining workers} = 45 - 15 = 30 \text{ workers}$$

Time = Remaining work / Remaining workers

$$\text{Time} = \frac{270 \text{ worker-days}}{30 \text{ workers}} = 9 \text{ days}$$

The remaining workers could take $\boxed{9 \text{ days}}$ to complete the work.

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The table shows marks obtained by a form three class in a certain school.
Marks (x): 2, 6, 8, 3, 1
No. of students (f): 9, 6, 8, 3, 1

Assuming the question asks for the mean mark:

The formula for the mean of a frequency distribution is $\bar{x} = \frac{\sum fx}{\sum f}$.

$$\bar{x} = \frac{128}{27}$$ $$\bar{x} \approx 4.7407$$

The mean mark is approximately $\boxed{4.74}$.