What is meant by significant figures ? Given any four rules for counting significant figures.

Explanation

### Step-by-Step Solution

1. **Definition of Significant Figures**:
Significant figures refer to the digits in a number that contribute to its precision. This includes all the non-zero digits, any zeros between significant digits, and any trailing zeros in a decimal number. The concept of significant figures helps in expressing the accuracy of a measurement.

2. **Rules for Counting Significant Figures**:
- **Rule 1**: Non-zero digits are always significant.
- Example: In the number 342.87, all digits (3, 4, 2, 8, 7) are significant. Thus, it has 5 significant figures.
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