A teacher recorded the amount of time taken by 21 students to complete a sprint race, to the nearest second, as follows:

■ Two students: between 51 and less than 56 seconds

■ Seven students: between 56 and less than 61 seconds

■ Eight students: between 61 and less than 66 seconds

■ Four students: between 66 and less than 71 seconds

Develop a table to estimate the sample mean and sample standard deviation for the recorded time using formulas (4.21) and (4.23).