To find the number of students in fifth grade, we can start with the number of students in third grade and use the information about the fourth and fifth grades.
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Number of students in third grade:
\[ \text{Third grade} = 231 \] -
Calculating the number of students in fourth grade:
There are 87 fewer students in fourth grade than in third grade.
\[ \text{Fourth grade} = \text{Third grade} - 87 = 231 - 87 = 144 \] -
Calculating the number of students in fifth grade:
There are 112 more students in fifth grade than in fourth grade.
\[ \text{Fifth grade} = \text{Fourth grade} + 112 = 144 + 112 = 256 \]
Thus, the number of students in fifth grade is \( \boxed{256} \).