Round off to 3 significant figures :
i) 20.93
ii) 0.0003125

Explanation

To round off the given numbers to 3 significant figures, we will follow these steps:

### Step 1: Round off 20.93 to 3 significant figures
1. Identify the significant figures in the number 20.93. The significant figures are 2, 0, 9, and 3, which means there are 4 significant figures in total.
2. Since we need to round this number to 3 significant figures, we look at the fourth significant figure, which is 3.
3. The digit after the last significant figure (9) is 3, which is less than 5. Therefore, we do not round up.
4. Thus, we keep the first three significant figures as they are: 20.9.

...