Let's begin by listing out the information given to us:
number of students (Mr Jones) = 30
number of students (Mr Smith) = 28
2 cups of juice per student
¾ cup of juice = 4 cups of water
Ratio of cup of juice to cup of water is:
[tex]\frac{3}{4}\colon4[/tex]There are a total of 58 students. That means they will need 116 cups of juice (2 per person). We will get the cups of water needed by:
[tex]\begin{gathered} \frac{3}{4}\colon4 \\ 116\colon x \\ \text{Cross multiply, we have:} \\ \frac{3}{4}x=116\cdot4 \\ 3x=116\cdot4\cdot4 \\ x=\frac{116\cdot4\cdot4}{3}=\frac{1856}{3} \\ x=618\frac{2}{3} \end{gathered}[/tex]They need 116 cup of juice and 618 2/3 cups of water