In positive numbers less than 1, the zeros between the decimal point and a non-zero number are blank significant

Explanation :

Digits that carry meaning which contributes to its measurement resolution are called significant figures.

In positive numbers less than 1, the zeros between the decimal point and a non-zero number are NOT significant.

For example,

In 0.0000208, the zeros before 2 has no significance. Hence, the significant figures are 3 i.e. 2, 0 and 8.

They are not significant.

Explanation:

The significant figures are the figures which are reliable in any measurement.

For example:

The number is 0.007709, the zeros between the decimal point and the first non zero digit, i.e., between decimal point and 2 are not significant. But the zero between the two non zero digit, i.e., between 7 and 9 is significant.

Thus, the number of significant figures are 4.  

a sonic boom is a loud boom that breaks the sound barrier

explanation: