Calculate the average reaction rate for the first 50s

Calculate the average reaction rate for the first 50s given:

Time (s): 0, 25, 50

Moles Mg (s): 0.55, 0.25, 0.14

Tº 0.55moles
T1, lost 0.3moles in 25s so, rate = 0.012moles/s
T2, lost another 0.11moles in 25s so, rate = 0.0044moles/s
over the entire 50s, there was a loss of 0.41moles for an overall average rate of 0.0082moles/s