The ages (in completed years) of members of a yoga club are tabulated in INCLUSIVE form: 21-30, 31-40, 41-50, 51-60, 61-70. A student insists that these must first be converted to the boundaries 20.5-30.5, 30.5-40.5, ... before the mean can be computed. Which statement is correct?

The boundary correction lowers the lower limit by 0.5 AND raises the upper limit by 0.5, so the two shifts cancel in $x_i=\frac{l+u}{2}$. The class marks 25.5, 35.5, 45.5, 55.5, 65.5 are identical both ways, so the mean is unaffected. (The correction does matter for the median and the mode, where the lower boundary $l$ is used on its own.) The other options assume the shift acts in only one direction.