To count significant figures we have to remember the following rules:
• All non zero digits are always significant.
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• Interior zeros, that is, zeros between non zero numbers are significant.
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• Leading zeros, that is, zeros at the beggining of the number are not significant.
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• Trailing zeros, that is, zeros at the end of the number are significant if and only if there is a decimal point present in the number.
With this rules we have that:
a)
Since in the number 13001 we have interior zeros and these are significant we have 5 significant figures.
b)
Since this number have all non zero numbers it has 5 significant rules.
c)
Since we have a decimal point the trailing zero count, hence we have 3 significant figures.
d)
In this case we have leading zeros this are not significant, therefore we have 2 significant figures.