Answer:
Option 3: 21 x 3/7
Explanation:
• The ratio of boys to girls = 3:4
,
• The number of members in the track team = 21
To find the number of boys on the team:
[tex]\begin{gathered} \text{ Number of boys}=\frac{\text{ The proportion of boys}}{Total\text{ proportion}}\times\text{ The number of members on the team} \\ \begin{equation*} =\frac{3}{3+4}\times21 \end{equation*} \\ =\frac{3}{7}\times21 \\ =21\times\frac{3}{7} \end{gathered}[/tex]
Therefore, the expression that can be used to find the number of boys on the team is:
[tex]21\times\frac{3}{7}[/tex]
The third option is correct.
