Answer: Algernon has left 850 centimeters of ribbon.
Explanation:
Given: Initially , Total length of ribbon = 25 meters
Since 1 meter = 100 centimeters, so total length of ribbon = 2500 centimeters
Now, ribbon used in first hour = 900 centimeters, ribbon used in second hour = 750 centimeters
Total ribbon used = 900 centimeters+ 750 centimeters
= 1650 centimeters
Ribbon left = 2500-1650= 850 centimeters
Hence, Algernon has left 850 centimeters of ribbon.