7. Convert \( \frac{2}{5} \) to a decimal. Round to the hundredths place if necessary. 0.25

a) \( \left(\frac{2}{5}-\frac{1}{7}\right):\left(\frac{1}{3}+\frac{21}{2}\right) \)

12. By selling an article for \( ₹ 1,200 \), a seller incurs a loss of \( 20 \% \). What should be the selling price of the same article if the seller wants to earn a profit of \( 20 \% \).

Consider the product \( 1 \times 2 \times 3 \times 4 \times \ldots \times 30 \). Determine the largest value of \( k \) such that \( 3^{k} \) is a factor of this product.

a) \( \left(\frac{1}{2}+\frac{2}{3}\right)^{2}= \)

3) \( \sqrt{8} \cdot \sqrt{8} \)