Simplify
(31/10) * (3/10) + (7/5) / 20

Answer: Option D

Explanation:

Let the boys are X, then girls are 7X, total = X+7X = 8X

So it should be multiple of 8, 30 is not a multiple of 8.

Answer: Option C

Explanation:

\begin{aligned}
\frac{\frac{7}{2}\div {\frac{5}{2}} \times {\frac{3}{2}} }{\frac{7}{2} \div { \frac{5}{2}} of \frac{3}{2} }\div 5.25
\end{aligned}

\begin{aligned}
= \frac{\frac{7}{2}\times {\frac{2}{5}} \times {\frac{3}{2}} }{\frac{7}{2} \div { \frac{15}{4}}}\div 5.25
\end{aligned}

\begin{aligned}
= \frac{\frac{21}{10}}
{\frac{7}{2} \times { \frac{4}{15}}}\div {\frac{525}{100}}
\end{aligned}

\begin{aligned}
= \frac{21}{10}\times{\frac{15}{14}}\times\frac{100}{525}

= \frac{6}{14}
= \frac{3}{7}
\end{aligned}

Answer: Option D

Answer: Option D

Answer: Option A