Answer:
5 classrooms
Step-by-step explanation:
We are given the total number of classrooms and the proportion that are for the kindergarteners and first graders. We can find the amount of classrooms that make up this amount and double it to get the amount of second and third grade classrooms. From there we can subtract that amount from the total amount of classes to get the amount of fourth and fifth grade classes.
Solving:
[tex]\subsection*{Total Number of Classrooms:}The total number of classrooms is:\[20 \, \text{classrooms}\]\subsection*{Classrooms for Kindergarteners and First Graders:}One-fourth of the total classrooms are for kinder and first grade:\[\frac{1}{4} \times 20 = \boxed{5 \, \text{classrooms}}\]\subsection*{Classrooms for Second and Third Grade}Twice as many classrooms are for second and third grade:\[2 \times 5 = \boxed{10 \, \text{classrooms}}\][/tex]
[tex]\subsection*{Classrooms for Fourth and Fifth Grade}The rest of the classrooms are for fourth and fifth grade. Therefore, we subtract the classrooms for the other grades from the total number of classrooms:\[20 - (5 + 10) = 20 - 15 =\boxed{ 5 \, \text{classrooms}}\][/tex]
The number of classrooms for fourth and fifth grades is 5 classrooms.