Five stopwatch timings of one pendulum swing: 2.01, 1.98, 2.03, 1.99, 2.02 s. A classmate reports the result as 1.98 s "because it was measured too". What is the right report?

A. The mean 2.01 s, with uncertainty from the spread

Averaging beats picking: random errors partially cancel in the mean, and the scatter (standard deviation ≈ 0.02 s) becomes the honest uncertainty: $T = 2.01 \pm 0.01$ s. Reporting spread is what separates a measurement from a guess.