High score
Input
95
Output
A
95 lies between 90 and 100 inclusive, so the grade is 'A'.
Full lesson preview
Classify Exam Grade
Convert a numerical exam score into a letter grade using conditional branching.
Python practice15 minControl Flow (If–Else Logic)IntermediateLast updated March 15, 2026
Problem statement
Write a function classify_grade(score) that takes a numeric score (int or float) and returns a letter grade according to the scale:
- 90 to 100 -> 'A'
- 80 to 89.999... -> 'B'
- 70 to 79.999... -> 'C'
- 60 to 69.999... -> 'D'
- 0 to 59.999... -> 'F'
If the score is outside the range 0 to 100, return the string 'Invalid score'. Use precise boundary handling so that 90.0 yields 'A', 89.999 yields 'B', etc.
Task
Implement grade classification using if/elif/else and handle invalid scores.
Examples
Input format
A single number (int or float) representing the score.
Output format
Return a string: one of 'A', 'B', 'C', 'D', 'F', or 'Invalid score'.
Constraints
Scores may be floats. Treat 0 <= score <= 100 as valid; everything else is invalid.
Samples
Sample 1
Input
89.5
Output
B
89.5 is >=80 and <90, so it's a 'B'.