If $\frac{1}{2}$ is added to a number and the sum is multiplied by $3,$ the result is $21.$ Then the number is (in $.5$)

$\left[ {8\left\{ {\left( {\frac{{21 \times \sqrt {\frac{9}{{441}}} }}{5} \text{ of } 60\% - \frac{1}{5}} \right) \times 625 + 7} \right\} \div 4} \right] = ?$

The sum of three numbers is $68$. If the ratio between the first and second is $2:3$ and that between the second and third is $5:3$,then the second number is

Which one is the largest among the fractions $\frac{5}{113}, \frac{7}{120}, \frac{13}{145}$ and $\frac{17}{160}$?

The greatest number among $\sqrt{5}, \sqrt[3]{4}, \sqrt[5]{2}, \sqrt[7]{3}$ is

$(0.83 \times 0.83 \times 0.83 + 0.17 \times 0.17 \times 0.17)$ is equal to ...........