Student A : Length of scale = 25 m
Least count = 0.5 cm = 0.005m
Student A can measure the length of 9.5m by using the scale only once so there will be an error of 0.005m in 9.5m
∴ Relative error
==0.0005 Student B : Length of scale : 1m = 100 cm
Least count = 0.05 cm
To measure 9.5m, student B has to use this meter scale atleast 10 times
∴ Relative error
=×10=0.005cm Student C : Length of scale : 1 foot = 30.48cm
Least count = 0.05 cm
To measure 9.5m, student C has to use this scale approximately 31 times
∴ Relative error
=×31=0.05cm ∴ Relative error is least for Student
A.