Subtract $2.5\times {10}^4$ from $3.9x{10}^5$ and give the answer to correct number of significant figures.

Add $2.384\times {10}^{-4}\to 1.7\times {10}^{-5}$ and express the result to correct number of significant figures.

Report the answer to correct significant figures in $2.5\times 1.25$

Subtract $4.5\times {10}^4\text{from}7.9\times {10}^5$ and express the result to an appropriate number of significant figures.

Give the number of significant figures
$2.653\times {10}^4$

Subtract 10.5 from 10.587 and express the result with correct number of significant figures.

State the number of significant figures in $2.67\times {10}^{-24}kg$