In order to measure the period of a single pendulum using a stop clock, a student repeated the experiment for $10$ times and noted down the time period for each experiment as $5.1, 5.0, 4.9, 4.9, 5.1, 5.0, 4.9, 5.1, 5.0, 4.9\, s$ . The correct way of expressing the result for the period is