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Four persons measure the length of a rod as 20.00 cm, 19.75 cm, 17.01 cm and 18.25 cm. The relative error in the measurement of average length of the rod is

Asked in JEE Main 23rd Jan 1st Shift 2026 · Mean and standard deviation of readings

Answer: (3) 0.06

Step-by-step solution

Readings: 20.00, 19.75, 17.01, 18.25 cm.

Mean: l=(75.01)/4=18.75 cm.

Deviations: 1.25, 1.00, 1.74, 0.50 cm.

Mean absolute deviation: Δl=(4.49)/4=1.12 cm.

Relative error: (1.12)/(18.75)=0.06.

Why the other options are wrong

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