I.  Significant Figures
•Rule 1: To determine the number of  significant figures in a measurement, read the number from left to right and count all digits, starting with the first non-zero digit.
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Rule 4: When a number is rounded off, the last digit to be retained is increased by one only if the following digit is 5 or more.
Rule 2: When adding or subtracting numbers, the number of decimal places in the answer should be equal to the number of decimal places in the number with the fewest places.
Rule 3: In multiplication or division, the number of significant figures in the answer should be the same as that in the quantity with the fewest significant figures.