(i) We know, 2.5 kg = 2500 g.
Required percentage = $\left(\frac{175}{2500} \times 100\right)$%
= $\frac{17500}{2500}$%
= 7%
Hence, 175 g is 7% of 2.5 kg.
(ii) To convert a fraction into a percentage, multiply it by 100 and put the % sign.
$\frac{3}{5} = \left(\frac{3}{5} \times 100\right)$%
= $\frac{300}{5}$%
= 60%
Hence, $\mathbf{\frac{3}{5}}$ expressed as percentage is 60%.
(iii) 6% of x = 0.21
$$\begin{aligned}\Rightarrow \frac{6}{100} \times x = 0.21\\[1em] \Rightarrow x = \frac{0.21 \times 100}{6}\\[1em] \Rightarrow x = \frac{21}{6}\\[1em] \Rightarrow x = 3.5\end{aligned}$$
Hence, if 6% of x is 0.21, then x = 3.5.
(iv) Percentage of marks = $\left(\frac{57}{150} \times 100\right)$%
= $\frac{5700}{150}$%
= 38%
Hence, Renu got 38% marks.
(v) Increase = 15% of ₹ 80
= $\frac{15}{100} \times 80$
= ₹ 12.
Increased amount = ₹ (80 + 12) = ₹ 92.
Hence, when ₹ 80 is increased by 15%, we get ₹ 92.
(vi) Decrease = 15% of ₹ 120
= $\frac{15}{100} \times 120$
= ₹ 18.
Decreased amount = ₹ (120 − 18) = ₹ 102.
Hence, ₹ 120 decreased by 15% = ₹ 102.