Zeros between non-zero digits are always significant
Leading zeros are never significant
Trailing zeros are only significant if the number contains a decimal point
Rounding Rules
When rounding significant figures the standard rules of rounding numbers apply, except that non-significant digits to the left of the decimal are replaced with zeros.
Example: 356 rounded to 2 significant digits is 360
This calculator rounds down if the next digit is less than 5 and rounds up when the next digit is greater than or equal to 5.
In the table below 305.459 is rounded from 0 to 6 significant figures. For comparison the same number is rounded from 0 to 6 decimal places. You can see the difference between rounding for significant figures and rounding to decimal places.
Jana could have bought any number greater than 3.5 because 3.5 is the middle of 3-4. If the amount of trail mix is closer to 4 pounds, the pounds she could have bought must be greater than 3.5 but less than 4 pounds.