The number of significant figures in $6.25 \times 10^5$ is

For an experimental expression $y=\frac{32.3 \times 1125}{27.4}$,where all the digits are significant. Then to report the value of $y$,we should write $:-$

$A$ length of $5.997 \ m$ rounded off to three significant figures is written as .......... $m$.

Explain: "By using significant digits,we can prevent unnecessarily long calculations."

$A$ student measuring the diameter of a pencil of circular cross-section with the help of a vernier scale records the following four readings: $5.50\, mm, 5.55\, mm, 5.45\, mm, 5.65\, mm$. The average of these four readings is $5.5375\, mm$ and the standard deviation of the data is $0.07395\, mm$. The average diameter of the pencil should therefore be recorded as:

If the length of a rod is measured as $830600 \ mm$, then the number of significant figures in the measurement is