The area of a square is $5.29\ cm^2$. The area of $7$ such squares taking into account the significant figures is ........... $cm^2$.

The mass of a box measured by a grocer's balance is $2.30 \ kg$. Two gold pieces of masses $20.15 \ g$ and $20.17 \ g$ are added to the box. What is
$(a)$ the total mass of the box,
$(b)$ the difference in the masses of the pieces to correct significant figures?

The uncertain digit in the measurement of a length reported as $41.68 \,cm$ is ...........

The mass and volume of a body are $4.237 \ g$ and $2.5 \ cm^3$,respectively. The density of the material of the body in correct significant figures is $:-$ (in $g \ cm^{-3}$)

$A$ person measures the mass of $3$ different particles as $435.42 \ g$,$226.3 \ g$,and $0.125 \ g$. According to the rules for arithmetic operations with significant figures,the sum of the masses of the $3$ particles will be: (in $g$)

Perform the subtraction considering significant figures: $3.9 \times 10^5 - 2.5 \times 10^4$