Explanation:

- Let's denote the initial number of students in the class as 'n'.

- The total weight of the original students is $68.5n$ kg.

- Four students with weights of 72.2 kg, 70.8 kg, 70.3 kg, and 66.7 kg join the class.

- The total weight for the 4 new students is 280 kg.

- With the new students, the total number of students becomes $n+4$.

- The problem states the average weight increases by 0.3 kg (300 g).

Let's solve the equation:

1. Initial total weight = $68.5n$.

2. New total weight = $68.5n+280$.

3. New average weight = $68.8$ kg ($68.5+0.3$).

Setting up the equation:

$$\frac{68.5n+280}{n+4}=68.8$$

Solving for $n$:

$$68.5n+280=68.8n+275.2$$

$$280-275.2=68.8n-68.5n$$

$$4.8=0.3n$$

$$n=\frac{4.8}{0.3}$$

$$n=16$$

- Option 1: 16 is the correct answer.

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