SIGNIFICANT FIGURES
The digits 1, 2, 3, 4, 5, 6, 7, 8 & 9 are always significant.

Zero is only significant if

it is between significant figures
or it is at the end of a number after the decimal point. 
The zeros at the END
of a whole number are NOT significant. The zeros BETWEEN other significant figures ARE significant. The zeros at the START of a decimal are NOT significant. A zero at the END of a decimal IS significant. 
2000
has 1 sig fig 9000001 has 7 sig fig 0.001 has 1 sig fig 0.00 has 1 sig fig 
PRACTICE 
MyMaths
