What is the mean absolute deviation of 25,24,25,23,20,18

The mean absolute deviation is the mean of the absolute values of the differences of the numbers from their mean. It is convenient to let a spreadsheet or calculator do the tedious math. Here it is by hand:

Total of given values: 135

Mean of given values: 135/6 = 22.5

Deviations of given values from the mean:

... {2.5, 1.5, 2.5, 0.5, - 2.5, - 4.5}

Absolute values of deviations from the mean:

... {2.5, 1.5, 2.5, 0.5, 2.5, 4.5}

Total of those: 14

Mean absolute deviation: 14/6 = 2 1/3.