what are significant numbers explain the rules to calculate these significant nunbers

A significant figure or number is that digit that carries meaning, contributing to its precision. This includes all digits except leading zeros where they serve merely as placeholders to indicate the scale of the number and spurious digits that are introduced.

Significant figures provide accuracy in the measurements. The significant digits of a number are meaningful or can be used confidently. The approximate results obtained from numerical methods can be confidently used by applying the criteria of significant figures.

Rules to determine the number of significant figures or numbers:

All non-zero digits are significant. Example: 160 mL has three significant figures.

Zeroes preceding the first non-zero digit are not significant. Example: 0.03692 has four significant figures.

Zeroes between two non-zero digits are significant. Example: 32.006 has five significant figures.

Zeroes at the end or right of a number are significant when they are on the right side of the decimal point. Example: 0.7400 has four significant figures.

Counting numbers of objects have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeros after placing a decimal. Example: 35 books can be represented as 35 = 35.00000000