The number 30 has 1 significant figure if written as "30" with no decimal point. However, if it is written with a decimal point, such as "30." or with trailing zeros after a decimal (e.g., "30.0"), then it would have more significant figures. But as simply "30," it is counted as having 1 significant figure because trailing zeros without a decimal point are not significant. This rule is based on the principle that trailing zeros are only significant if the number contains a decimal point.